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Text File | 1995-12-29 | 7.0 KB | 252 lines

; Example 6: Interrupts. ; This example illustrates the use of an interrupt handler. ; To use it, you must turn on the "Use I/O Services" in the ; Options menu. You might want to run the program at ; "Fastest" speed with the Memory Display set to "Graphics". ; The program is really a combination of two previous ; examples, Example 3 and Example 5. The computer runs ; the program from example 3. However, when you type a ; character, an "interrupt handler" is called to process ; the character you typed. The processing is the same as ; what is done in Example 5. What the user of the program ; sees is the calculator program of Example 5, with the ; powers-of-three program from Example 3 running in the ; "background". ; For the best effect, run the program at Fastest speed in ; Graphics memory display mode. Type numbers separated by ; "+", "-", and "=". @PC 0 ; Make sure the PC contains 0, the starting location ; of the program. 1024# 0 ; Clear memory before loading @0 ; Start loading program at location 0 lod-c 0 ; Set up the starting state sto num sto sum lod-c '+ sto op inh calc ; Now, set up an interrupt handler at ; location calc. The computer will jump ; to this location to handle characters ; typed by the user. jmp bkg ; Jump to the "background" program at ; location "bkg"; this program is ; executed only if there is no input ; to be processed. ;------------------------------------------------------------ @100 ; Load the calculator program at location 100 calc: gtc ; Get a typed character from the input queue; ; there HAS to be one, since the compuer only ; jumps to this location when a character ; has been typed sto ch ; Save the typed character in "ch". sub-c '+ ; Test the typed character. If it is jmz do_op ; +, -, or =, then jump to "do_op". lod ch ; If it is a digit between 0 and 9, sub-c '- ; jump to "digit". Otherwise, it is jmz do_op ; illegal input; jump to "bad". lod ch sub-c '= jmz do_op lod ch sub-c '0 jmn bad lod ch sub-c '9 jmn digit jmz digit bad: lod-c '? ; Illegal input was typed. Output the ptc ; chatacter "?" followed by a space, lod-c 32 ; then return the calculator to its ptc ; starting state. jmp restart digit: lod ch ; A digit was typed. sub-c '0 ; Convert the character to the corresponding sto ch ; number and put that number back in ch. lod num ; Set num := 10*num + ch, effectively adding shl ; the typed digit onto the end of num. shl ; (10*num is computed by shifting num shl ; left three times, giving 8*num, and add num ; then adding num twice to that.) add num add ch sto num rti ; After processing the input digit, end ; the interrupt handler with a return- ; from-interrupt instruction do_op: lod num ; A "+", "-", or "=" was typed. Output ptu ; the current value of "num", and then lod op ; either add "num" to "sum" or subtract sub-c '+ ; it from "sum", depending on the jmz plus ; pending operation, "op". minus: lod sum sub num sto sum jmp fin_op plus: lod sum add num sto sum fin_op: lod-c 0 ; After the calculation, "num" is reset to 0 sto num ; so that the user can start typing the lod ch ; next number. "Ch", the operation that ptc ; was just input, is printed. sub-c '= ; If "ch" is "+" or "-", then it is jmz equals ; stored in "op" to become the next lod ch ; pending operation. sto op rti ; Return-from-interrupt equals: lod sum ; If the typed character was "=", then ptu ; the final answer, "sum" is output, lod-c 32 ; followed by a space (ASCII 32) to ptc ; separate computations in the output list. jmp restart ; Then the calculator is returned to its ; starting state to get ready for the ; next computation. restart: lod-c 0 ; Restore the starting state of the calculator sto num ; and return from the interrupt handler sto sum lod-c '+ sto op rti op: data ; Pending operation, that is, a "+" or "-" ; that will be performed after its second ; operand has been entered. ch: data ; Holds the character typed most recently ; by the user. num: data ; Holds a number as itis being typed by ; the user. sum: data ; Holds the result of any computation ; performed so far, while the user is ; typing the next number. ;------------------------------------------------------------ @300 ; Load the "background" program at location 200 bkg: lod-c 3 ; The program itself... sto N1 lod-c 1 sto ct1 copy: lod ct1 sto ct2 sto ct lod-c N1 sto src lod-c N2 sto dest c1: lod-i src sto-i dest lod ct dec jmz sm sto ct lod src dec sto src lod dest dec sto dest jmp c1 sm: lod ct2 sto ct lod-c N2 sto src lod-c N1 sto dest lod-c 0 sto carryQ s1: lod-i dest add-i src sto-i dest jmf cr1 s2: lod-i dest add-i src sto-i dest jmf cr2 s3: lod ct dec jmz copy sto ct lod src dec sto src lod dest dec sto dest jmp s1 cr1: lod-c s2 sto return jmp add1 cr2: lod-c s3 sto return jmp add1 add1: lod ct sto aCt lod dest sto aDest a1: lod aDest dec sto aDest lod aCt dec sto aCt jmz advnc lod-i aDest add-c 1 sto-i aDest jmf a1 jmp-i return advnc: lod carryQ jmz adv1 lod-i aDest add-c 1 sto-i aDest jmp-i return adv1: lod ct1 inc sto ct1 lod-c 1 sto-i aDest lod-c 1 sto carryQ jmp-i return return:data ; Data locations used by the program in its ct1: data ; calculations ct2: data ct: data src: data dest: data aCt: data aDest: data carryQ:data @700 ; "N1" will refer to location 700 N1: data @1000 ; "N2" will refer to location 1000 N2: data