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** Programmer's Technical Reference for MSDOS and the IBM PC ** ┌─────────────────────────────┐ │ Shareware Version, 10/26/90 │ │ Please Register Your Copy │ └─────────────────────────────┘ Copyright (c) 1987, 1990 Dave Williams USA copyright TXG 392-616 ISBN 1-878830-02-3 (disk-based text) C H A P T E R F I V E Interrupts 22h Through 86h note: the registered version of this chapter is more than twice this size. Interrupt 22h Terminate Address (0:0088h) This interrupt transfers control to the far (dword) address at this interrupt location when an application program terminates. The default address for this interrupt is 0:0088h through 0:008Bh. This address is copied into the program's Program Segment Prefix at bytes 0Ah through 0Dh at the time the segment is created and is restored from the PSP when the program terminates. The calling program is normally COMMAND.COM or an application. Do not issue this interrupt directly, as the EXEC function call does this for you. If an application spawns a child process, it must set the Terminate Address prior to issuing the EXEC function call, otherwise when the second program terminated it would return to the calling program's Terminate Address rather than its own. This address may be set with int 21, function 25h. Interrupt 23h Ctrl-Break Exit Address (0:008Ch) If the user enters a Ctrl-Break during STDIN, STDOUT, STDPRN, or STDAUX, int 23h is executed. If BREAK is on, int 23h is checked on MOST function calls (notably 06h). If the user written Ctrl-Break routine saves all registers, it may end with a return-from-interrupt instruction (IRET) to continue program execution. If the user-written interrupt program returns with a long return, the carry flag is used to determine whether the program will be aborted. If the carry flag is set, the program is aborted, otherwise execution continues (as with a return by IRET). If the user-written Ctrl-Break interrupt uses function calls 09h or 0Ah, (Display String or Buffered Keyboard Input) then a three-byte string of 03h-0Dh-0Ah (ETX/CR/LF) is sent to STDOUT. If execution is continued with an IRET, I/O continues from the start of the line. When the interrupt occurs, all registers are set to the value they had when the original function call to DOS was made. There are no restrictions on what the Ctrl-Break handler is allowed to do, including DOS function calls, as long as the registers are unchanged if an IRET is used. If the program creates a new segment and loads a second program which itself changes the Ctrl-Break address, the termination of the second program and return to the first causes the Ctrl-Break address to be restored from the PSP to the value it had before execution of the second program. Interrupt 24h Critical Error Handler (0:0090h) When a critical error occurs within DOS, control is transferred to an error handler with an int 24h. This may be the standard DOS error handler (ABORT, RETRY, IGNORE) or a user-written routine. On entry to the error handler, AH will have its bit 7=0 (high order bit) if the error was a disk error (probably the most common error), bit 7=1 if not. BP:SI contains the address of a Device Header Control Block from which additional information can be retrieved (see below). The register is set up for a retry operation and an error code is in the lower half of the DI register with the upper half undefined. These are the error codes: The user stack is in effect and contains the following from top to bottom: IP DOS registers from issuing int 24h CS int 24h flags AX user registers at time of signal BX int 21h request CX DX SI DI BP DS ES IP from original int 21h CS flags To reroute the critical error handler to a user-writen critical error handler, the following should be done: Before an int 24h occurs: 1) The user application initialization code should save the int 24h vector and replace the vector with one pointing to the user error routine. When the int 24h occurs: 2) When the user error routine received control it should push the flag registers onto the stack and execute a far call to the original int 24h vector saved in step 1. 3) DOS gives the appropriate prompt, and waits for user input (Abort, Retry, Ignore, Fail). After the user input, DOS returns control to the user error routine instruction following the far call. 4) The user error routine can now do any tasks nescessary. To return to the original application at the point the error occurred, the error routine needs to execute an IRET instruction. Otherwise, the user error routine should remove the IP, CS, and flag registers from the stack. Control can then be passed to the desired point. Int 24h provides the following values in registers on entry to the interrupt handler: entry AH status byte (bits) 7 0 disk I/O hard error 1 other error - if block device, bad FAT - if char device, code in DI 6 unused 5 0 if IGNORE is not allowed 1 if IGNORE is allowed 4 0 if RETRY is not allowed 1 if RETRY is allowed 3 0 if FAIL is not allowed 1 if FAIL is allowed 2 \ disk area of error 00 = DOS area 01 = FAT 1 / 10 = root dir 11 = data area 0 0 if read operation 1 if write operation AL drive number if AH bit 7 = 1, otherwise undefined If it is as hard error on disk (AH bit 7=0), register AL contains the failing drive number (0=A:, 1=B:, etc.). BP:SI address of a Device Header Control Block for which error occurred block device if high bit of BP:SI+4 = 1 low byte of DI: error code (note: high byte is undefined) error code description 00h attempt to write on write-protected diskette 01h unknown unit 02h drive not ready 03h unknown command 04h data error (bad CRC) 05h bad request structure length 06h seek error 07h unknown media type 08h sector not found 09h printer out of paper 0Ah write fault 0Bh read fault 0Ch general failure 0Fh invalid disk change (DOS 3.x+) 10h (DOS 3.x) FCB unavailable 11h (DOS 3.x) sharing buffer overflow The handler must return this information: The registers are set such that if an IRET is executed, DOS responds according to (AL) as follows: AL 00h ignore the error 01h retry the operation 02h terminate via int 22h 03h fail the system call that is in progress (DOS 3.x+) note 1) Be careful when choosing to ignore a response because this causes DOS to beleive that an operation has completed successfully when it may not have. 2) If the error was a character device, the contents of AL are invalid. OTHER ERRORS If AH bit 7=1, the error occurred on a character device, or was the result of a bad memory image of the FAT. The device header passed in BP:SI can be examined to determine which case exists. If the attribute byte high-order bit indicates a block device, then the error was a bad FAT. Otherwise, the error is on a character device. If a character device is involved, the contents of AL are unpredictable, the error code is in DI as above. Notes: 1. Before giving this routine control for disk errors, DOS performs several retries. The number of retries varies according to the DOS version. 2. For disk errors, this exit is taken only for errors occurring during an int 21h function call. It is not used for errors during an int 25h or 26h. 3. This routine is entered in a disabled state. 4. All registers must be preserved. 5. This interrupt handler should refrain from using DOS function calls. If necessary, it may use calls 01h through 12h. Use of any other call destroys the DOS stack and leaves DOS in an unpredictable state. 6. The interrupt handler must not change the contents of the device header. 7. If the interrupt handler handles errors itself rather than returning to DOS, it should restore the application program's registers from the stack, remove all but the last three words on the stack, then issue an IRET. This will return to the program immediately after the int 21h that experienced the error. Note that if this is done DOS will be in an unstable state until a function call higher than 12h is issued, therefore not recommended. 8. For DOS 3.x, IGNORE requests (AL=0) are converted to FAIL for critical errors that occur on FAT or DIR sectors. 9. For DOS 3.10 up, IGNORE requests (AL=0) are converted to FAIL requests for network critical errors (50-79). The device header pointed to by BP:SI is as follows: DWORD Pointer to next device (0FFFFh if last device) WORD Attributes: Bit 15 1 if character device. If bit 15 is 1: Bit 0 = 1 if current standard input Bit 1 = 1 if current standard output Bit 2 = 1 if current NULL device Bit 3 = 1 if current CLOCK device 0 if block device Bit 14 is the IOCTL bit WORD pointer to device driver strategy entry point WORD pointer to device driver interrupt entry point 8-BYTE character device named field for block devices. The first byte is the number of units. To tell if the error occurred on a block or character device, look at bit 15 in the attribute field (WORD at BP:SI+4). If the name of the character device is desired, look at the eight bytes starting at BP:SI+10. HANDLING OF INVALID RESPONSES (DOS 3.x) A) If IGNORE (AL=0) is specified by the user and IGNORE is not allowed (bit 5=0), make the response FAIL (AL=3). B) If RETRY (AL=1) is specified by the user and RETRY is not allowed (bit 4=0), make the response FAIL (AL=3). C) If FAIL (AL=3) is specified by the user and FAIL is not allowed (bit 3=0), make the response ABORT. (AL=2) Interrupt 25h Absolute Disk Read Interrupt 26h Absolute Disk Write (0:0094h, 0:0098h) These transfer control directly to the device driver. On return, the original flags are still on the stack (put there by the INT instruction). This is necessary because return information is passed back in the current flags. The number of sectors specified is transferred between the given drive and the transfer address. Logical sector numbers are obtained by numbering each sector sequentially starting from track 0, head 0, sector 1 (logical sector 0) and continuing along the same head, then to the next head until the last sector on the last head of the track is counted. Thus, logical sector 1 is track 0, head 0, sector 2; logical sector 2 is track 0, head 0, sector 3; and so on. Numbering then continues wih sector 1 on head 0 of the next track. Note that although the sectors are sequentially numbered (for example, sectors 2 and 3 on track 0 in the example above), they may not be physically adjacent on disk, due to interleaving. Note that the mapping is different from that used by DOS 1.10 for dual-sided diskettes. The request is as follows: int 25 for Absolute Disk Read, int 26 for Absolute Disk Write entry AL drive number (0=A:, 1=B:, etc) CX number of sectors to read DS:BX disk transfer address (buffer) DX first relative sector to read - beginning logical sector number return CF set if error AL error code issued to int 24h in low half of DI AH 01h bad command 02h bad address mark 03h write-protected disk 04h requested sector not found 08h DMA failure 10h data error (bad CRC) 20h controller failed 40h seek operation failed 80h attachment failed to respond note 1) Original flags on stack! Be sure to pop the stack to prevent uncontrolled growth 2) Ints 25 and 26 will try rereading a disk if they get an error the first time. 3) All registers except the segment registers are destroyed by these calls Interrupt 25h ABSOLUTE DISK READ (except DOS 4.0/Compaq DOS 3.31 >32M partition) entry AL drive number (0=A, 1=B, etc) DS:BX pointer to Disk Transfer Address (buffer) CX number of sectors to read DX first relative sector to read return CF 1 if error AL error code issued to int 24h in low half of DI AH 80h attachment failed to respond 40h seek operation failed 20h controller failed 10h data error (bad CRC) 08h DMA failure 04h requested sector not found 03h write-protected disk 02h bad address mark 01h bad command note Original flags on stack! Interrupt 25h DOS 4.0/Compaq DOS 3.31 - ABSOLUTE DISK READ (>32M hard-disk partition) entry AL drive number (0=A, 1=B, etc) CX 0FFFFh DS:BX Packet address DWORD sector number WORD number of sectors to read DWORD transfer address return same as above? note Partition is potentially >32Mb (and requires this form of the call) if bit 1 of device attribute word in device driver is set Interrupt 26h ABSOLUTE DISK WRITE (except DOS 4.0/Compaq DOS 3.31 >32M partition) entry AL drive number (0=A, 1=B, etc) DS:BX pointer to Disk Transfer Address (buffer) CX number of sectors to write DX first relative sector to write return CF 1 if error AL error code issued to int 24h in low half of DI AH same error codes as for int 25h note Original flags on stack! Interrupt 26h DOS 4.0/Compaq DOS 3.31 - ABSOLUTE DISK WRITE (>32M hard disk partitions) entry AL drive number (0=A, 1=B, etc) CX 0FFFFh DS:BX Packet address DWORD sector number WORD number of sectors to write DWORD transfer address return same as above? note Partition is potentially >32M (and requires this form of the call) if bit 1 of device attribute word in device driver is set Interrupt 27h Terminate And Stay Resident (0:009Ch) (obsolete) This vector is used by programs that are to remain resident when COMMAND.COM regains control. After initializing itself, the program must set DX to its last address plus one relative to the program's initial DS or ES value (the offset at which other programs can be loaded), then execute interrupt 27h. DOS then considers the program as an extension of itself, so the program is not overlaid when other programs are executed. This is useful for loading programs such as utilities and interrupt handlers that must remain resident. entry CS current program segment DX last program byte + 1 return none note 1) This interrupt must not be used by .EXE programs that are loaded into the high end of memory. 2) This interrupt restores the interrupt 22h, 23h, and 24h vectors in the same manner as interrupt 20h. Therefore, it cannot be used to install permanently resident Ctrl-Break or critical error handler routines. 3) The maximum size of memory that can be made resident by this method is 64K. 4) Memory can be more efficiently used if the block containing a copy of the environment is deallocated before terminating. This can be done by loading ES with the segment contained in 2Ch of the PSP, and issuing function call 49h (Free Allocated Memory). 5) DOS function call 4Ch allows a program to pass a completion code to DOS, which can be interpreted with processing (see function call 31h). 6) Terminate and stay resident programs do not close files. 7) Int 21, function 31h is the preferred method to cause a program to remain resident because this allows return information to be passed and allows a program larger than 64K to remain resident. Interrupt 28h (not documented by Microsoft) * DOS Idle Interrupt Int 28h has been provided by DOS since release 2.0. The int 28h process is similar to the "Timer Tick" process provided by BIOS via int 1Ch in that it is an "outbound" (from DOS) call which an application can "hook onto" to get service at a particular entry point. DOS normally only issues int 28h when it recieves a function call (int 21h) from a foreground application with an argument in the range of 0 thru 12 (0Ch) in the AH register, or when it is idling waiting for keyboard input. In effect, when DOS issues int 28h, it is saying to the background task "I'm not doing anything hot right now, if you can use the time, go ahead." This means that a foreground application which doesn't do many low-number DOS functions can preempt CPU time easily. It is possible, if you are careful, to enhance the background priority by providing more int 28h calls than DOS normally would issue. When int 28h is being issued it is usually safe to do DOS calls. You won't get int 28hs if a program is running that doesn't do its keyboard input through DOS. You should rely on the timer interrupt for these. It is used primarily by the PRINT.COM routines, but any number of other routines can be chained to it by saving the original vector and calling it with a FAR call (or just JMPing to it) at the end of the new routine. Int 28h is not called at all when any non-trivial foreground task is running. As soon as a foreground program has a file open, int 28h no longer gets called. Could make a good driver for for a background program that works as long as there is nothing else going on in the machine. DOS uses 3 separate internal stacks: one for calls 01h through 0Ch; another for calls 0Dh and above; and a third for calls 01h through 0Ch when a Critical Error is in progress. When int 28h is called, any calls above 0Ch can be executed without destroying the internal stack used by DOS at the time. The byte which is pushed on the stack before an int 28h just indicates which stack area is being used by the current int 21h call. In DOS 3.1, the code sequence that calls int 28h looks like this: PUSH SS:[0304] INT 28 POP SS:[0304] The low-order byte of the word pushed contains 1 if the int 21h call currently in progress is for services 1 through 0Ch, and 0 for service 0 and for 0Dh and up. Assuming that the last DOS call was not a reentrant one, this tells you which set of DOS services should be safe to call. If the InDOS flag is zero on int 28h, then it was called by someone other than DOS, and the word on the stack should NOT be examined. entry no parameters availible return none note 1) The int 28h handler may invoke any int 21h function except functions 00h through 0Ch (and 50h/51h under DOS 2.x unless DOS CritErr flag is set). 2) Apparently int 28h is also called during screen writes 3) Until some program installs its own routine, this interrupt vector simply points to an IRET opcode. 4) Supported in OS/2 1.0's DOS Compatibility Box Interrupt 29h (not documented by Microsoft) * Internal - Quick Screen Output This method is extremely fast (much faster than DOS 21h subfunctions 2 and 9, for example), and it is portable, even to "non-compatible" MS-DOS computers. entry AL character to output to screen return unknown note 1) Documented by Digital Research's DOS Reference as provided with the DEC Rainbow 2) If ANSI.SYS is installed, character output is filtered through it. 3) Works on the IBM PC and compatibles, Wang PC, HP-150 and Vectra, DEC Rainbow, NEC APC, Texas Instruments PC and others 4) This interrupt is called from the DOS's output routines if output is going to a device rather than a file, and the device driver's attribute word has bit 3 (04h) set to "1". 5) This call has been tested with MSDOS 2.11, PCDOS 2.1, PCDOS 3.1, PCDOS 3.2, and PCDOS 3.3. 6) Used in IBMBIO.COM as a vector to int 10, function 0Eh (write TTY) followed by an IRET. Interrupt 2Ah Microsoft Networks - Session Layer Interrupt * (not documented by Microsoft) entry AH 00h check to see if network BIOS installed return AH <> 0 if installed 01h execute NETBIOS request 02h set net printer mode 03h get shared-device status (check direct I/O) AL 00h DS:SI pointer to ASCIIZ disk device name return CF 0 if allowed 04h execute NETBIOS AL 0 for error retry 1 for no retry ES:BX pointer to network control block return AX 0 for no error AH 1 if error AL error code 05h get network resource information AL 00h return AX reserved BX number of network names CX number of commands DX number of sessions 06h Network Print-stream Control note NETBIOS 1.10 20h unknown note AL=01h intercepted by DESQview 2.0 80h Begin DOS Critical Section AL 1 to 6 81h End DOS Critical Section AL 1 to 6 82h Server Hook return unknown note called by the int 21h function dispatcher in DOS 3.10+ for function 0 and functions greater than 0Ch except 59h 84h keyboard busy loop note similar to DOS's int 28h Interrupt 2Bh (not documented by Microsoft) * Unknown - Internal Routine for DOS (IRET) Interrupt 2Ch (not documented by Microsoft) * Unknown - Internal Routine for DOS (IRET) Interrupt 2Dh (not documented by Microsoft) * Unknown - Internal Routine for DOS (IRET) Interrupt 2Eh (undocumented by Microsoft) (DOS 2.0+) * Internal Routine for DOS (Alternate EXEC) This interrupt passes a command line addressed by DS:SI to COMMAND.COM. The command line must be formatted just like the unformatted parameter area of a Program Segment Prefix. That is, the first byte must be a count of characters, and the second and subsequent bytes must be a command line with parameters, terminated by a carriage return character. When executed, int 2Eh will reload the transient part of the command interpreter if it is not currently in memory. If called from a program that was called from a batch file, it will abort the batch file. If executed from a program which has been spawned by the EXEC function, it will abort the whole chain and probably lock up the computer. Int 2Eh also destroys all registers including the stack pointer. Int 2Eh is called from the transient portion of the program to reset the DOS PSP pointers using the above Functions #81 & #80, and then reenters the resident program. When called with a valid command line, the command will be carried out by COMMAND.COM just as though you had typed it in at the DOS prompt. Note that the count does not include the carriage return. This is an elegant way to perform a SET from an application program against the master environment block for example. entry DS:SI pointer to an ASCIIZ command line in the form: count byte ASCII string carriage return null byte note 1) Destroys all registers including stack pointer 2) Seems to work OK in both DOS 2.x and 3.x 3) It is reportedly not used by DOS. 4) As far as known, int 2Eh is not used by DOS 3.1, although it was called by COMMAND.COM of PCDOS 3.0, so it appears to be in 3.1 only for the sake of compatibility. Interrupt 2Fh Multiplex Interrupt Interrupt 2Fh is the multiplex interrupt. A general interface is defined between two processes. It is up to the specific application using interrupt 2Fh to define specific functions and parameters. This interrupt is becoming more commonly used as the availible interrupt 21 functions are getting to be in short supply. Int 2Fh doesn't require any support from DOS itself for it to be used in application programs. It's not handled by DOS, but by the programs themselves. Every multiplex interrupt handler is assigned a specific multiplex number. The multiplex number is specified in the AH register; the AH value tells which program your request is directed toward. The specific function that the handler is to perform is placed in the AL register. Other parameters are places in the other registers as needed. The handlers are chained into the 2Fh interrupt vector and the multiplex number is checked to see if any other application is using the same multiplex number. There is no predefined method for assigning a multiplex number to a handler. You must just pick one. To avoid a conflict if two applications choose the same multiplex number, the multiplex numbers used by an application should be patchable. In order to check for a previous installation of the current application, you can search memory for a unique string included in your program. If the value you wanted in AH is taken but you don't find the string, then another application has grabbed that location. Int 2Fh was not documented under DOS 2.x. There is no reason not to use int 2Fh as the multiplex interrupt in DOS 2.x. The only problem is that DOS 2.x does not initialize the int 2Fh vector, so when you try to chain to it like you are supposed to, it will crash. If your program checks the vector for being zero and initializes it itself or doesn't chain in that case, it will work for you n 2.x just the same as 3.x. Function 01h PRINT.COM Register AH identifies which program is to handle the interrupt. Values 00h-7Fh are reserved for DOS, not that anyone cares much. Values 0C0h-0FFh are reserved for applications. Register AL contains the function code if used entry AH 01h AL 00h PRINT Get Installed State This call must be defined by all int 2Fh handlers. It is used by the caller of the handler to determine if the handler is present. On entry, AL=0. On return, AL contains the installed state as follows: return AL 0FFh installed 01h not installed, not OK to install 00h not installed, OK to install 01h PRINT Submit File DS:DX pointer to submit packet format byte level dword pointer to ASCIIZ filename return CF set if error AX error code note 1) A submit packet contains the level (BYTE) and a pointer to the ASCIIZ string (DWORD in offset:segment form). The ASCIIZ string must contain the drive, path, and filename of the file you want to print. The filename cannot contain global filename characters. return CF set if error AX error code 02h PRINT Cancel File On entry, AL=2 and DS:DX points to the ASCIIZ string for the print file you want to cancel. Global filename characters are allowed in the filename. DS:DX pointer to ASCIIZ file name to cancel (wildcards OK) return CF set if error AX error code 03h PRINT remove all files return CF set if error AX error code 04h PRINT hold queue/get status This call holds the jobs in the print queue so that you can scan the queue. Issuing any other code releases the jobs. On entry, AL=4. On return, DX contains the error count. DS:SI points to the print queue. The print queue consists of a series of filename entries. Each entry is 64 bytes long. The first entry in the queue is the file currently being printed. The end of the queue is marked by the entry having a null as the first character. return DX error count DS:SI pointer to print queue (null-string terminated list of 64-byte ASCIIZ filenames) CF set if error AX error code 01h function invalid 02h file not found 03h path not found 04h too many open files 05h access denied 08h queue full 09h spooler busy 0Ch name too long 0Fh drive invalid 05h PRINT restart queue return CF set if error AX error code Function 05h DOS 3.x critical error handler entry AH 05h AL 00h installation check return AL 00h not installed, OK to install 01h not installed, can't install 0FFh installed note This set of functions allows a user program to partially or completely override the default critical error handler in COMMAND.COM AL 01h handle error - nonzero error code in AL return CF clear ES:DI pointer to ASCIIZ error message CF set use default error handler AL (?) Function 06h ASSIGN entry AH 06h 00h installation check return AH <> 0 if installed 01h get memory segment return ES segment of ASSIGN work area Function 10h SHARE entry AH 10h AL 00h installation check return AL 00h not installed, OK to install 01h not installed, not OK to install 0FFh installed Function 11h Multiplex - network redirection entry AH 11h AL 00h installation check return AL 00h not installed, OK to install 01h not installed, not OK to install 0FFh installed 01h-05h unknown 06h close remote file 07h-09h unknown 0Ah unknown stack word (?) return CF set on error 0Bh unknown stack word (?) return CF set on error(?) 0Ch unknown 0Dh unknown 0Eh unknown stack word (?) return (?) 0Fh-16h unknown 17h unknown stack word (?) return (?) 18h unknown stack word (?) return (?) 19h-1Dh unknown 1Eh do redirection stack word function to execute return CF set on error 1Fh printer setup stack word function(?) return CF set on error(?) 20h-25h unknown stack word (?) 26h unknown Function 12h multiplex, DOS 3.x internal services entry AH 12h AL 00h installation check return AL 0FFh for compatibility with other int 2Fh functions 01h close file (?) stack word value - unknown return BX unknown CX unknown ES:DI pointer to unknown value note Can be called only from within DOS 02h get interrupt address stack word vector number return ES:BX pointer to interrupt vector stack unchanged 03h get DOS data segment return DS segment of IBMDOS.COM file 04h normalize path separator stack word character to normalize return AL normalized character (forward slash turned to backslash) stack unchanged 05h output character stack word character to output return stack unchanged note Can be called only from within DOS 06h invoke critical error return AL 0-3 for Abort, Retry, Ignore, Fail note Can be called only from within DOS 07h move disk buffer (?) DS:DI pointer to disk buffer return buffer moved to end of buffer list note Can be called only from within DOS 08h decrement word ES:DI pointer to word to decrement return AX new value of word note Word pointed to by ES:DI decremented, skipping zero 09h unknown DS:DI pointer to disk buffer(?) return (?) note Can be called only from within DOS 0Ah unknown note Can be called only from within DOS 0Bh unknown ES:DI pointer to system file table entry(?) return AX (?) note Can be called only from within DOS 0Ch unknown note Can be called only from within DOS 0Dh get date and time return AX current date in packed format DX current time in packed format note Can be called only from within DOS 0Eh do something to all disk buffers (?) return DS:DI pointer to first disk buffer note can be called only from within DOS 0Fh unknown DS:DI pointer to (?) return DS:DI pointer to (?) note 1) Can be called only from within DOS 2) Calls on function 1207h 10h find dirty/clean(?) buffer DS:DI pointer to first disk buffer return DS:DI pointer to first disk buffer which has (?) flag clear ZF clear if found set if not found 11h normalize ASCIIZ filename DS:SI pointer to ASCIIZ filename to normalize ES:DI pointer to buffer for normalized filename return destination buffer filled with uppercase filename, with slashes turned to backslashes 12h get length of ASCIIZ string ES:DI pointer to ASCIIZ string return CX length of string 13h uppercase character stack word character to convert to uppercase return AL uppercase character stack unchanged 14h compare far pointers DS:SI first pointer ES:DI second pointer return ZF set if pointers are equal ZF clear if not equal 15h unknown DS:DI pointer to disk buffer stack word (?) return stack unchanged note Can be called only from within DOS 16h get address of system FCB BX system file table entry number return ES:DI pointer to system file table entry 17h set default drive (?) stack word drive (0=A:, 1=B:, etc) return DS:SI pointer to drive data block for specified drive stack unchanged note Can be called only from within DOS 18h get something (?) return DS:SI pointer to (?) 19h unknown stack word drive (0=default, 1=A:, etc) return (?) stack unchanged note 1) Can be called only from within DOS 2) Calls function 1217h 1Ah get file's drive DS:SI pointer to filename return AL drive (0=default, 1=A:, etc, 0FFh=invalid) 1Bh set something (?) CL unknown return AL (?) note Can be called only from within DOS 1Ch checksum memory DS:SI pointer to start of memory to checksum CX number of bytes DX initial checksum return DX checksum note Can be called only from within DOS 1Dh unknown DS:SI pointer to (?) CX (?) DX (?) return AX (?) CX (?) DX (?) 1Eh compare filenames DS:SI pointer to first ASCIIZ filename ES:DI pointer to second ASCIIZ filename return ZF set if filenames equivalent clear if not 1Fh build drive info block stack word drive letter return ES:DI pointer to drive info block (will be overwritten by next call) stack unchanged note Can be called only from within DOS 20h get system file table number BX file handle return CF set on error, error code in AL AL 06h (invalid file handle) CF clear if successful byte ES:[DI] = system file table entry number for file handle 21h unknown DS:SI pointer to (?) return (?) note Can be called only from within DOS 22h unknown SS:SI pointer to (?) return nothing(?) note Can be called only from within DOS 23h check if character device (?) return DS:SI pointer to device driver with same name as (?) note Can be called only from within DOS 24h delay return after delay of (?) ms note Can be called only from within DOS 25h get length of ASCIIZ string DS:SI pointer to ASCIIZ string return CX length of string Function 43h Microsoft Extended Memory Specification (XMS) Function 5453h TesSeRact Standard for Ram-Resident Program Communication Function 64h SCRNSAV2.COM entry AH 64h AL 00h installation check return AL 00h not installed 0FFh installed note SCRNSAV2.COM is a screen saver for PS/2's with VGA by Alan Ballard Function 7Ah Novell NetWare entry AH 7Ah AL 00h installation check note 1) Returns address of entry point for IPX and SPX 2) Parameters are listed under int 21 Function 087h APPEND entry AH 087h AL 00h APPEND installation check return AH <> 0 if installed 01h APPEND - unknown 02h APPEND - version check Function 088h Microsoft Networks entry AH 088h AL 00h network program installation check return AH <> 0 if installed BX installed component flags (test in this order!) bit 6 server bit 2 messenger bit 7 receiver bit 3 redirector 01h unknown 02h unknown 03h get current POST address return ES:BX POST address 04h set new POST address ES:BX new POST address 09h network version check Function 0AAh VIDCLOCK.COM entry AH 0AAh AL 00h installation check return AL 00h not installed 0FFh installed note VIDCLOCK.COM is a memory-resident clock by Thomas G. Hanlin III Function 0BBh Network Functions entry AH 0BBh AL 00h net command installation check 01h, 02h unknown 03h get server POST address 04h get server POST address Function 0F7h AUTOPARK.COM (PD TSR hard disk parking utility) entry AH 0F7h AL 00h installation check return AL 00h not installed 0FFh installed note AUTOPARK is a TSR HD parker by Alan D. Jones 01h set parking delay BX:CX 32 bit count of 55ms timer ticks MSDOS 2Fh functions 01h (PRINT), 02h (ASSIGN), 10h (SHARE): return AX Error Codes Description 01h invalid function number 02h file not found 03h path not found 04h too many open files 05h access denied 06h invalid handle 08h queue full 09h busy 0Ch name too long 0Fh invalid drive was specified CF clear (0) if OK set (1) if error - error returned in AX note 1) The multiplex numbers AH=0h through AH=7Fh are reserved for DOS. Applications should use multiplex numbers 80h through 0FFh. 2) When in the chain for int 2Fh, if your code calls DOS or if you execute with interrupts enabled, your code must be reentrant/recursive. 3) Important! In versions of DOS prior to 3.0, the int 2Fh vector was initialized to zero rather than being pointed into the DOS service area. You must initialize this vector manually under DOS 2.x. ┌─────────────────────────────────────────────────────────────────────────────┐ │ Miscellaneous Interrupts - in numerical order │ └─────────────────────────────────────────────────────────────────────────────┘ Interrupt 30h (not a vector!) far jump instruction for CP/M-style calls Interrupt 31h Unknown note The CALL 5 entry point does a FAR jump to here Interrupt 32h Unknown Interrupt 33h Used by Microsoft Mouse Driver Function Calls Function Requests 00h Reset Driver and Read Status entry AH 00h return AH status 0 hardware/driver not installed -1 hardware/driver installed BX number of buttons -1 two buttons 0 other than two 3 Mouse Systems mouse 01h Show Mouse Cursor entry AH 01h return unknown 02h Hide Mouse Cursor entry AH 02h return unknown note multiple calls to hide the cursor will require multiple calls to function 01h to unhide it. 03h Return Position and Button Status entry AH 03h return BX button status bit 0 left button pressed if 1 bit 1 right button pressed if 1 bit 2 middle button pressed if 1 (Mouse Systems mouse) CX column DX row 04h Position Mouse Cursor entry AH 04h CX column DX row return unknown 05h Return Button Press Data entry AH 05h BX button 0 left 1 right 2 middle (Mouse Systems mouse) return AH button states bit 0 left button pressed if 1 bit 1 right button pressed if 1 bit 2 middle button pressed if 1 (Mouse Systems mouse) BX no. of times specified button pressed since last call CX column at time specified button was last pressed DX row at time specified button was last pressed 06h Return Button Release Data entry AH 06h BX button 0 left 1 right 2 middle (Mouse Systems mouse) return AH button states bit 0 left button pressed if 1 bit 1 right button pressed if 1 bit 2 middle button pressed if 1 (Mouse Systems mouse) BX no. of times specified button released since last call CX column at time specified button was last released DX row at time specified button was last released 07h Define Horizontal Cursor Range entry AH 0007h CX minimum column DX maximum column return unknown 08h Define Vertical Cursor Range entry AH 08h CX minimum row DX maximum row return unknown 09h Define Graphics Cursor entry AH 09h BX column of cursor hot spot in bitmap (-16 to 16) CX row of cursor hot spot (-16 to 16) ES:DX pointer to bitmap 16 words screen mask 16 words cursor mask return unknown note Each word defines the sixteen pixels of a row, low bit rightmost 0Ah Define Text Cursor entry AH 0Ah BX hardware/software text cursor 00h software CX screen mask DX cursor mask 01h hardware CX start scan line DX end scan line return unknown note When the software cursor is selected, the char/attribute data at the current screen position is ANDed with the screen mask and the with the cursor mask 0Bh Read Motion Counters entry AH 0Bh return CX number of mickeys mouse moved horiz. since last call DX number of mickeys mouse moved vertically note 1) A mickey is the smallest increment the mouse can sense. Positive values indicate up/right 0Ch Define Interrupt Subroutine Parameters entry AH 0Ch CX call mask bit bit 0 call if mouse moves bit 1 call if left button pressed bit 2 call if left button released bit 3 call if right button pressed bit 4 call if right button released bit 5 call if middle button pressed (Mouse Systems) bit 6 call if middle button released (Mouse Systems) ES:DX address of FAR routine return unknown note when the subroutine is called, it is passed these values: AH condition mask (same bit assignments as call mask) BX button state CX cursor column DX cursor row DI horizontal mickey count SI vertical mickey count 0Dh Light Pen Emulation On entry AH 0Dh return unknown 0Eh Light Pen Emulation Off entry AH 0Eh return unknown 0Fh Define Mickey/Pixel Ratio entry AH 0Fh CX number of mickeys per 8 pixels horizontally DX number of mickeys per 8 pixels vertically return unknown 10h Define Screen Region for Updating entry AH 10h CX,DX X,Y coordinates of upper left corner SI,DI X,Y coordinates of lower right corner return unknown note Mouse cursor is hidden during updating, and needs to be explicitly turned on again 11h not documented by Microsoft 12h Set Large Graphics Cursor Block AH 12h BH cursor width in words CH rows in cursor BL horizontal hot spot (-16 to 16) CL vertical hot spot (-16 to 16) ES:DX pointer to bit map of screen and cursor maps return AH -1 if successful note PC Mouse. Not documented by Microsoft 13h Define Double-Speed Threshold entry AH 13h DX threshold speed in mickeys/second, 0 = default of 64/second return unknown note If speed exceeds threshold, the cursor's on-screen motion is doubled 14h Exchange Interrupt Subroutines entry AH 14h return unknown 15h Return Drive Storage Requirements entry AH 15h return BX size of buffer needed to store driver state 16h Save Driver State entry AH 16h ES:DX pointer to buffer return unknown 17h Restore Driver State entry AH 17h ES:DX pointer to buffer containing saved state return unknown 18h-1Ch not documented by Microsoft; unknown 1Dh Define Display Page Number entry AH 1Dh 1Eh Return Display Page Number entry AH 1Eh return unknown 42h PCMouse - Get MSmouse Storage Requirements AH 42h return AX 0FFFFh successful BX buffer size in bytes for functions 50h and 52h 00h MSmouse not installed 42h functions 42h, 50h, and 52h not supported 52h PCMouse - Save MSmouse State entry AH 50h BX buffer size ES:DX pointer to buffer return AX 0FFFFh if successful 52h PCMouse - restore MSmouse state entry AH 52h BX buffer size ES:DX pointer to buffer return AX 0FFFFh if successful Int 33: In addition, the following functions are appended to BIOS int 10h and implemented as the EGA Register Interface Library: 0F0h read one register 0F1h write one register 0F2h read consecutive register range 0F3h write consecutive register range 0F4h read non-consecutive register set 0F5h write non-consecutive register set 0F6h revert to default register values 0F7h define default register values 0FAh get driver status Interrupt 34h Turbo C/Microsoft languages - Floating Point emulation This interrupt emulates opcode 0D8h Interrupt 35h Turbo C/Microsoft languages - Floating Point emulation This interrupt emulates opcode 0D9h Interrupt 36h Turbo C/Microsoft languages - Floating Point emulation This interrupt emulates opcode 0DAh Interrupt 37h Turbo C/Microsoft languages - Floating Point emulation This interrupt emulates opcode 0DBh Interrupt 38h Turbo C/Microsoft languages - Floating Point emulation This interrupt emulates opcode 0DCh Interrupt 39h Turbo C/Microsoft languages - Floating Point emulation This interrupt emulates opcode 0DDh Interrupt 3Ah Turbo C/Microsoft languages - Floating Point emulation This interrupt emulates opcode 0DEh Interrupt 3Bh Turbo C/Microsoft languages - Floating Point emulation This interrupt emulates opcode 0DFh Interrupt 3Ch Turbo C/Microsoft languages - Floating Point emulation This int emulates instructions with an ES segment override Interrupt 3Dh Turbo C/Microsoft languages - Floating Point emulation This interrupt emulates a standalone FWAIT instruction Interrupt 3Eh Turbo C/Microsoft languages - Floating Point emulation Interrupt 3Fh Overlay manager interrupt (Microsoft LINK.EXE) Default overlay interrupt; may be changed with LINK switch Interrupt 40h Hard Disk BIOS Pointer to disk BIOS entry when a hard disk controller is installed. The BIOS routines use int 30h to revector the diskette handler (original int 13h) here so int 40 may be used for hard disk control Interrupt 41h Hard Disk Parameters (XT,AT,XT2,XT286,PS except ESDI disks) Pointer to first Hard Disk Parameter Block, normally located in the controller card's ROM. This table may be copied to RAM and changed, and this pointer revectored to the new table. note 1) format of parameter table is: dw cylinders db heads dw starting reduced write current cylinder (XT only, 0 for others) db maximum ECC burst length db control byte bits 0-2 drive option (XT only, 0 for others) bit 3 set if more than 8 heads bit 4 always 0 bit 5 set if manufacturer's defect map on max cylinder+1 bit 6 disable ECC retries bit 7 disable access retries db standard timeout (XT only, 0 for others) db formatting timeout (XT only, 0 for others) db timeout for checking drive (XT only, 0 for others) dw landing zone (AT, PS/2) db sectors/track (AT, PS/2) db 0 2) normally vectored to ROM table when system is initialized. Interrupt 42h Pointer to screen BIOS entry (EGA, VGA, PS/2) Relocated (by EGA, etc.) video handler (original int 10h). Revectors int 10 calls to EGA BIOS. Interrupt 43h Pointer to EGA graphics character table. The POST initializes this vector pointing to the default table located in the EGA ROM BIOS. (PC-2 and up). Not initialized if EGA not present. This vector was referred to (mistakenly) as the Video Parameters table in the original EGA BIOS listings. Interrupt 44h Pointer to graphics character table. This table contains the (0:0110h) dot patterns for the first 128 characters in video modes 4,5, and 6, and all 256 characters in all additional graphics modes. Not initialized if EGA not present. 2) EGA/VGA/CONV/PS - EGA/PCjr fonts, characters 00h to 7Fh 3) Novell NetWare - High-Level Language API 4) This interrupt is not used by some EGA cards. Interrupt 45h Reserved by IBM (not initialized) Interrupt 46h Pointer to second hard disk, parameter block (AT, XT/286, PS/2) (see int 41h) (except ESDI hard disks) (not initialized unless specific user software calls for it) Interrupt 47h Reserved by IBM (not initialized) Interrupt 48h Cordless Keyboard Translation (PCjr, XT [never delivered]) (0:0120h) This vector points to code to translate the cordless keyboard scancodes into normal 83-key values. The translated scancodes are then passed to int 9. (not initialized on PC or AT) Interrupt 49h Non-keyboard Scan Code Translation Table Address (PCjr) (0:0124h) This interrupt is used for operation of non-keyboard devices on the PCjr, such as the Keystronic Numeric Keypad. This interrupt has the address of a table used to translate non-keyboard scancodes (greater than 85 excepting 255). This interrupt can be revectored by a user application. IBM recommends that the default table be stored at the beginning of an application that required revectoring this interrupt, and that the default table be restored when the application terminates. (not initialized on PC or AT) The PCjr BIOS can interpret scancodes other than those generated by the keyboard to allow for expansion. The keyboard generates scancodes from 01h to 055h, including 0FFh. Any scancodes above 55h (56h through 7Eh for make codes and 0D6h through 0FEh for break codes) are processed in the following manner: 1) if the incoming make code falls within the range of the translate table whose address is pointed to by int 49h, it is translated into the corresponding scancode. Any incoming break codes above 0D5h are ignored. 2) if the new translated scancode ius less and 56h, it is processed by the BIOS as a keyboard scancode and the same data is placed in the BIOS keyboard buffer. 3) if the translated scancode is higher than 55h or the incoming scancode is outside the range of the translate table, 40h is added creating a new extended scancode. The extended scancode is placed in the BIOS keyboard buffer with the character code of 00h (NUL). This utilitizes the range of 96h through 0BEh for scancodes 56h through 7Eh. The default translate-table maps scancodes 56h through 6Ah to existing keyboard values. Codes 6Bh theough 0BEh are mapped (by adding 40h) to extended codes 0ABh through 0FEh since they are outside the range of the default translate table. The format of the translate table is: 0 length - the number of nonkeyboard scancodes that are mapped within the table (from 1 to n) 1 to n word high byte 00h (NUL) byte scancode with low order byte representing the scancode mapped values relative to their input values within the range of 56h through 7Eh With this layout, all keyboard scancodes can be intercepted through int 9h and and nonkeyboard scancodes can be intercepted through int 48h. Interrupt 4Ah Real-Time Clock Alarm (Convertible, PS/2) (not initialized on PC or AT) Invoked by BIOS when real-time clock alarm occurs Interrupt 4Bh Reserved by IBM (not initialized) Interrupt 4Ch Reserved by IBM (not initialized) Interrupt 4Dh Reserved by IBM (not initialized) Interrupt 4Eh Reserved by IBM (not initialized) Used instead of int 13h for disk I/O on TI Professional PC Interrupt 4Fh Reserved by IBM (not initialized) Interrupt 50-57 IRQ0-IRQ7 relocated by DesQview (normally not initialized) Interrupt 58h Reserved by IBM (not initialized) Interrupt 59h Reserved by IBM (not initialized) GSS Computer Graphics Interface (GSS*CGI) DS:DX Pointer to block of 5 array pointers return CF 0 AX return code CF 1 AX error code note 1) Int 59 is the means by which GSS*CGI language bindings communicate with GSS*CGI device drivers and the GSS*CGI device driver controller. 2) Also used by the IBM Graphic Development Toolkit Interrupt 5Ah Reserved by IBM (not initialized) Interrupt 5Bh Reserved by IBM (not initialized) Interrupt 5Ah Cluster Adapter BIOS entry address (normally not initialized) Interrupt 5Bh Reserved by IBM (not initialized) (cluster adapter?) Interrupt 5Ch NETBIOS interface entry port ES:BX pointer to network control block return AL error code (0 if none) note 1) When the NETBIOS is installed, interrupts 13 and 17 are interrupted by the NETBIOS; interrupt 18 is moved to int 86 and one of int 2 or 3 is used by NETBIOS. Also, NETBIOS extends the int 15 function 90 and 91h functions (scheduler functions) 2) Normally not initialized. 3) TOPS network card uses DMA 1, 3 or none. Interrupt 5Dh Reserved by IBM (not initialized) Interrupt 5Eh Reserved by IBM (not initialized) Interrupt 5Fh Reserved by IBM (not initialized) Interrupt 60h-67h User Program Interrupts (availible for general use) Various major programs make standardized use of this group of interrupts. Details of common use follows Interrupt 60h 10-Net Network entry AH 11h Lock and Wait AL drive number or 0 DX number of seconds to wait ES:SI Ethernet address or 0 DS:BX pointer to 31-byte ASCIIZ semaphore name return AL status 0 successful 1 timeout 2 server not responding 3 invalid semaphore name 4 semaphore list is full 5 invalid drive ID 6 invalid Ethernet address 7 not logged in 8 write to network failed 9 semaphore already logged for this CPU entry AH 12h Lock AL drive number or 0 for default ES:SI Ethernet address or 0 DS:BX pointer to 31-byte ASCIIZ semaphore name return AL status (see function 11h) 1 semaphore currently logged note Unlike function 11h, this function returns immediately entry AH 13h Unlock AL drive number or 0 ES:SI Ethernet address or 0 DS:BX pointer to 31-byte ASCIIZ semaphore name return AL status (see function 11h) 1 semaphore not logged Interrupt 67h Used by Lotus-Intel-Microsoft Expanded Memory Specification user and Ashton-Tate/Quadram/AST Enhanced Expanded Memory specification (See Chapter 10) Interrupt 68h Not Used (not initialized) Interrupt 69h Not Used (not initialized) Interrupt 6Ah Not Used (not initialized) Interrupt 6Bh Not Used (not initialized) Interrupt 6Ch System Resume Vector (Convertible) (not initialized on PC) DOS 3.2 Realtime Clock update Interrupt 6Dh Not Used (not initialized) Interrupt 6Eh Not Used (not initialized) Interrupt 6Fh Novell NetWare - PCOX API (3270 PC terminal interface) Interrupt 6Fh 10-Net Network API entry AH 00h Login DS:DX login record 8 bytes user name 8 bytes password 12 bytes name of super-station return CL security level AX status 0000h good login 0FF01h no response from superstation 0FF02h network error 0FF03h invalid password 0FF04h no local buffer 0FF05h superstation not available 0FF06h node already logged in 0FF07h login not valid from this node 0FF08h node ID already in use 01h Logoff return CX number of files closed AX status 0000h successful 0FF08h superstation ID not already logged in 02h Status of node DS:DX pointer to 512-byte record 8 bytes user name (0 if none) byte station type 0 workstation 1 superstation 4 logged into multiple superstations 24 bytes list of superstations logged into more than one superstation 12 bytes node ID word message count for this station (send for user node, receive for superstations) for superstations only: word drives allocated (bit 0=A:, bit 1=B:,...) byte user service flag bit 4: SUBMIT is on 3: mail waiting for node 2: calendar waiting for you 1: news waiting for you 0: mail waiting for you byte printers allocated (bit 0=LPT1,...) byte number of unprinted spool files byte number of opened files byte number of logged on files byte primary drive (1=A:) byte reserved n bytes list of logged on node IDs (each 12 bytes, max 38 IDs) return CF set on error AX error code 0FF01h no response from node 0FF02h network error 0FF04h no local buffer 0FF16h invalid node ID 03h Get Address of Configuration Table return ES:BX pointer to record (actually starts at [BX-25]) word count of dropped Send6F word buffer start address word comm driver base address word send/receive retry count byte number of 550ms loops word UFH address word CDIR address word LTAB address word SFH address word FTAB address word RLTAB address word SMI address word NTAB address ES:BX pointer to word address of first CT_DRV byte number of DRV entries 8 bytes login name 12 bytes node ID 6 bytes node address byte flag byte CT_CFLG bit 1: sound bell bit 0: CHAT permit byte CT_PSFLG bit 5: PRINT permit bit 4: KB initiated bit 3: CHAT called FOXPTRM bit 2: SUBMIT active bit 1: SUBMIT received bit 0: SUBMIT permit byte reserved word receive message count word send message count word retry count word failed count word driver errors word dropped responses/CHATs 9 bytes list ID/NTAB address (3 entries-LPT1-3?) 6 bytes AUX ID/NTAB address (2 entries-COM1-2?) byte active CB channel byte received 6F messages on queue 9 bytes activity counters for channels 1-9 04h Send DS:BX pointer to record 12 bytes receiving node's ID word length of data at DX DS:DX pointer to data (max 1024 bytes) return CF set on error AX error code 0FF01h timeout 0FF02h network error 0FF04h no local buffer 0FF16h invalid parameter (bad length) 05h Receive CX number of seconds before timeout DS:DX pointer to receive buffer 12 bytes sending node's ID word length of message n bytes message (maximum 1024 bytes) return CF set on error AX error code 0FF01h timeout 0FF18h sent message has been dropped 06h Unknown 07h Lock Handle BX file handle CX:DX starting offset in file SI record length return CF set on error AX error code 0FF01h timeout 02h file not found 0FF17h record locked by another user 08h Unlock Handle BX file handle AL mode 0 unlock all 1 unlock record at CX:DX return CF set on error AX error code 02h file not found 0Bh Lock Semaphore, Return Immediately AL drive number or 0 ES:SI Ethernet address or 0 DS:BX pointer to 31-byte ASCIIZ semaphore name return AL status 0 successful 1 semaphore currently locked 2 server not responding 3 invalid semaphore name 4 semaphore list is full 5 invalid drive ID 6 invalid Ethernet address 7 not logged in 8 write to network failed 9 semaphore already logged in this CPU 0Ch unlock semaphore AL drive number or 0 ES:SI Ethernet address or 0 DS:BX pointer to 31-byte ASCIIZ semaphore name return AL status (see AH=0Bh) 1 semaphore not locked 0Dh Who CX length of data DS:DX pointer to array of records to be filled 12 bytes node ID byte flag (1=workstation, 2=superstation) return CL number of records returned (responding stations) 0Eh spool/print DS:DX pointer to record word 0 initiate spool 1 abort print 2 close spool 3 delete spool 4 print 5 get report info 11 bytes file name byte notification bit 6: do ID page bit 5: no form feed bit 3: notify at print completion bit 2: notify at print start and reply? bit 1: notify at print start bit 0: no notification byte days to keep (0FFh=forever) byte device (1=LPT1) word length of following data area n bytes $SCNT records returned if code in first word is 05h return CF set on error AX error code 0FF16h invalid parameter 0FF17h device not mounted 0FF18h already spooling to named device 11h Lock FCB AL mode 0 sequential 1 random 2 random block DS:DX pointer to FCB return CF set on error AX 02h file not found 0FF01h timeout 0FF17h record locked by another user 12h Unlock FCB AL mode 0 sequential 1 random 2 random block DS:DX pointer to FCB return CF set on error AX 02h file not found Interrupt 70h IRQ 8, Real Time Clock Interrupt (AT, XT/286, PS/2) Interrupt 71h IRQ 9, Redirected to IRQ 8 (AT, XT/286, PS/2) LAN Adapter 1 (rerouted to int 0Ah [IRQ2] by BIOS) Interrupt 72h IRQ 10 (AT, XT/286, PS/2) Reserved Interrupt 73h IRQ 11 (AT, XT/286, PS/2) Reserved Interrupt 74h IRQ 12 Mouse Interrupt (PS/2) Interrupt 75h IRQ 13, Coprocessor Error, BIOS Redirect to int 2 (NMI) (AT) Interrupt 76h IRQ 14, Hard Disk Controller (AT, XT/286, PS/2) Interrupt 77h IRQ 15 (AT, XT/286, PS/2) Reserved Interrupt 78h Not Used Interrupt 79h Not Used Interrupt 7Ah Novell NetWare - LOW-LEVEL API Interrupt 7Bh-7Eh Not Used Interrupt 7Fh unknown Used by second copy of COMMAND set with SHELL= Not used by COMMAND /C at DOS prompt Interrupt 80h-85h Reserved by BASIC note interrupts 80h through ECh are apparently unused and not initialized. Interrupt 86h Relocated by NETBIOS int 18 Interrupt 86h-0F0h Used by BASIC when BASIC interpreter is running Intrerrupt 0E0h CP/M-86 function calls Interrupt 0E4h Logitech Modula-2 v2.0 MONITOR entry AX 05h monitor entry 06h monitor exit BX priority Interrupt 0F0h unknown Used by secondary copy of COMMAND when SHELL= set Not used by COMMAND /C at DOS prompt Interrupts 0F1h-0FFh (absolute addresses 3C4-3FF) Location of Interprocess Communications Area Interrupt 0F8h Set Shell Interrupt (OEM) Set OEM handler for int 21h calls from 0F9h through 0FFh entry AH 0F8h DS:DX pointer to handler for Functions 0F9h thru 0FFh note 1) To reset these calls, pass DS and DX with 0FFFFh. DOS is set up to allow ONE handler for all 7 of these calls. Any call to these handlers will result in the carry bit being set and AX will contain 1 if they are not initialized. The handling routine is passed all registers just as the user set them. The OEM handler routine should be exited through an IRET. 2) 10 ms interval timer (Tandy?) Interrupt 0F9h First of 8 SHELL service codes, reserved for OEM shell (WINDOW); use like HP Vectra user interface? Interrupt 0FAh USART ready (RS-232C) Interrupt 0FBh USART RS ready (keyboard) Interrupt 0FCh Unknown Interrupt 0FDh reserved for user interrupt Interrupt 0FEh AT/XT286/PS50+ - destroyed by return from protected mode Interrupt 0FFh AT/XT286/PS50+ - destroyed by return from protected mode