MASM / TASM compatibility


Syntax of Emu8086 is fully compatible with all major assemblers including MASM and TASM;   though some directives are unique to Emu8086.   If required to compile using any other assembler you may need to comment out these directives, and any other directives that start with a '#' sign: 
#MAKE_COM#
#MAKE_EXE#
#MAKE_BIN#
#MAKE_BOOT#


Emu8086 does not support the ASSUME directive, actually most programmers agree that this directive just causes some mess in your code.   Manual attachment of CS:, DS:, ES: or SS: segment prefixes is preferred, and required by Emu8086 when data is in segment other then DS. For example: 
MOV AX, [BX]        ; same as MOV AX, DS:[BX]
MOV AX, ES:[BX]


Emu8086 does not require to define segment when you compile a COM file, though MASM and TASM may require this, for example:


CSEG    SEGMENT     ; code segment starts here.

; #MAKE_COM#        ; uncomment for Emu8086.

ORG 100h

start:  MOV AL, 5   ; some sample code...
        MOV BL, 2
        XOR AL, BL
        XOR BL, AL
        XOR AL, BL

        RET

CSEG    ENDS        ; code segment ends here.

END     start       ; stop compiler, and set entry point.


Entry point for COM file should always be at 0100h (first instruction after ORG 100h directive), though in MASM and TASM you may need to manually set an entry point using END directive. Emu8086 works just fine, with or without it.

In order to test the above code, save it into test.asm file (or any other) and run these commands from command prompt:

For MASM 6.0:
  MASM test.asm
  LINK test.obj, test.com,,, /TINY
For TASM 4.1:
  TASM test.asm
  TLINK test.obj /t
We should get test.com file (11 bytes), right click it and select Send To and emu8086. You can see that the disassembled code doesn't contain any directives and it is identical to code that Emu8086 produces even without all those tricky directives.


A template used by Emu8086 to create EXE files is fully compatible with MASM and TASM, just comment out #MAKE_EXE# directive to avoid Unknown character error at line 11.

EXE files produced by MASM are identical to those produced by emu8086.   TASM does not calculate the checksum, and has slightly different EXE file structure, but it produces quite the same machine code.

Note: there are several ways to encode the same machine instructions for the 8086 CPU, so generated machine code may vary when compiled on different compilers.


Emu8086 assembler supports shorter versions of BYTE PTR and WORD PTR, these are: B. and W.

For MASM and TASM you have to replace B. and W. with BYTE PTR and WORD PTR accordingly.

For example: 
LEA BX, var1
MOV WORD PTR [BX], 1234h ; works everywhere.
MOV w.[BX], 1234h        ; same instruction, but works in Emu8086 only.
HLT

var1  DB  0
var2  DB  0