Hi, I'm not an assembly coder, but I know enough to be dangerous. 🙈😜
Anyway first please check the CMP instruction parameters and you'll find that it takes 2 arguments a register or memory address and an immediate or 2 register/memory addresses. When you write addr equ 369h You are not creating a label (memory address) but instead it's a mnemonic for a numeric value. So basically the assembler will simply substitute all instances of addr with the number 369h. This means that your cmp statement which was cmp byte ptr [addr], 18h Is converted to cmp byte ptr [369h], 18h And this is not a valid instruction. Instead you want to use addr as offset or load it in a register to use it. I think this should work. xor bx, bx cmp byte ptr [bx+addr], 18h You really should read up on how equ and labels work. You might also want to define a data segment so you don't need to use the org statements to intermingle data and code (unless tou have to). Also get your hands on the borland turbo assembler manuals, or switch to masm and read its programming manual or watch videos to learn more about how labels and pointers work in assembly. Hope this helps, --Wolf On Sat, May 31, 2025, 20:55 hms--- via Freedos-user < freedos-user@lists.sourceforge.net> wrote: > Hi there > Not a specific FreeDos question, but related. I recently disassembled a DOS > .COM utility using "IDA Free", to see if I could make some minor mods. > I am brand new to 8086 assembly language and looking for an answer. > In the example test code below, I want to replace the instruction "cmp > byte_369, 18h" > with "cmp byte ptr [addr], 18h" or similar. I get an error message of > "Illegal immediate". > Do I need to use an intermediate instruction to achieve this? > The assembler is Borland's TASM. > Any help appreciated. > Thanks, John > > ; ------------------------------------------ > > SOURCE: > > .386 > .model tiny > > addr equ 369h > > seg000 segment byte public 'CODE' use16 > assume cs:seg000 > org 100h > assume es:nothing, ss:nothing, ds:seg000, fs:nothing, gs:nothing > public start > > start proc near > jmp here > > org 369h > byte_369 db 18h > > org 1234h > here: > cmp byte ptr [addr], 18h > cmp byte_369, 18h > > start endp > seg000 ends > end start > ; ------------------------------------------ > > EDITED ASSEMBLER OUTPUT: (for brevity) > > 8 org 100h > 13 0100 E9 1131 jmp here > 14 > 15 org 369h > 17 0369 18 byte_369 db 18h > 18 > 19 org 1234h > 21 1234 here: > > 22 1234 80 3E 0369 18 cmp byte ptr [addr],18h > **Error** test.ASM(22) Illegal immediate > > 23 1239 80 3E 0369r 18 cmp byte_369,18h > > ; end doc > > > > _______________________________________________ > Freedos-user mailing list > Freedos-user@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/freedos-user >
_______________________________________________ Freedos-user mailing list Freedos-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-user
