Hi

I have a problem with the following assembly language program and the related
questions.  Could anyone please help?  I am new to assembly language and have
been told that some of the instructions are illegal.

LABEL    EQU    00400H              ;Array start address
TOTAL    EQU    20H                   ;Number of items in the array
              MOV    CX,TOTAL         ;Set counter to register
              MOV    SI,LABEL          ;Set index register
LOOP:    MOV    AH,00H             ;1
              INT      16H                   ;2
              MOV    [SI],AL              ;3
              ADD     SI,1                  ;Increment array address
              SUB     [CX],1               ;Decrement loop counter
              JNZ      LOOP               ;Jump for next item
              END                             ;Assembler directive

The questions are
1 - Write down suitable text for the missing comments 1 to 3
2 - There is one deliberate error in the program where the instruction does not
match the comment.  Explain the error and write down the correct instruction.
JNZ should be JMP
3 - Describe in a sentence or two the overall fuction of the program.
4 - Which instructions can a LOOPNZ instruction replace.

If some of these instructions are illegal - I don't know which - any help would
be greatly appreciated.  Thanks.

Will.

1: AH=00h selects the "read keystroke" function of INT 16h.
2: call to BIOS keyboard service: returns the ASCII code of
   a key in AL.
3: Stores the ASCII code (AL) in the data segment at offset pointed
   to by SI.

SUB [CX],1 should be SUB CX,1 (or why not just DEC CX?)...

No, except if you want to create an infinite loop...

Reads 32 (TOTAL) characters from the keyboard buffer and stores them
in a buffer starting at DS:SI.

LOOPNZ LOOP could replace SUB CX,1 and JNZ LOOP...

Did I just do your homework? :-)

Take care,
Bartosz Dietrich