I've realized that there are certain instructions (that I never use myself) do not seem to assemble with FASM. For example, with DOS DEBUG, you have a difference between these two instructions, but FASM only has one. See, if you assemble this with DOS DEBUG:

cmp word ptr [0100h],1

you get

cmp word ptr [0100h],+1

which is opcode 83 3e 00 01 01

If I attempt to assemble the same thing in FASM, with the proper syntax, that is:

cmp word [0100h],1

I get opcode 81 3e 00 01 01 00

In DOS DEBUG, we can force such an opcode by assembling:

cmp word [0100h], word 1

So I understand that FASM makes default in "word" for this instruction. But when I try to assemble this in FASM:

cmp word [0100h],byte 1

I get an error message telling me that operator sizes mismatch.

HOW CAN I GET THAT INSTRUCTION ASSEMBLED WITH FASM????? [/i]

i tried,

and i got
80 3E 00 01 01 --- CMP BYTE PTR [0100],01
in debug.

vbVeryBeginner, but that is not the same, you are comparing just one byte against 1 instead of a word against 1.

Anyway with "cmp word [0100h], 1" I get

83 3E 00 01 01 CMP WORD PTR [0100],+01

I'm using FASM 1.65.21

Yes, "cmp word [0100h],1" makes:
83 3E 00 01 01
unlike what Cas wrote.

And it's "cmp word [0100h],word 1" that makes:
81 3e 00 01 01 00

You're right. I'm using an older version of FASM! I'll try the new one

Anyway, now that I'm here, let me give you a different example:

what about:

add sp,+1

where +1 is stored as a byte in DEBUG? I have not tested this one in FASM, but I expect the same as with the other one. I am going to test both with the new one. If it works fine with FASM 1.65.21, please ignore my post.

I appreciate you help very much, guys.

Even with older versions of fasm it was exactly the same way - you must have done something wrong if you've got different result.
The "add sp,1" makes shorter form, while "add sp,word 1" forces the longer one. See fasm's manual, section 1.2.6.

You're right. I've found what I did wrong.Sorry for the false alarm, and thank you so much for your assistance!