CODEWITHSUNDEEP
assemblyx86-16machine-code
Ba5t14n
Ba5t14n

Reputation: 739

Coverting Assembler (8086) Command Into Machine Code

I need to translate the Assembler command MOV BL,[ALPHA] into machine code of intels 8086 processor. Therefore, ALPHA is an 1 Byte variable at the 11th Position of the Data Segment, which is already loaded in the DS Register.

I already translated MOV AL,[ALPHA] in another task I've got. Here I found the MOV AL/AX,addr in the instruction set table so I could translate the whole thing into 1010|0000 1010|0000 or A0 10 in machine code.

I tend to use MOV r/m1,r/m2 of the instruction set table, but I am not 100% sure because I got problems when selecting the r/m part. Since this is the preparation for an exam I would be really happy if someone could help :)

Upvotes: 1

Views: 2681

Answers (1)

Jester
Jester

Reputation: 58762

That must be a strange instruction set table because there is no mov r/m1,r/m2 (you can't have two memory references). Better try the official intel one. What you need is mov r8, r/m8. The encoding for that is 8A /r. Using Table 2-1. 16-Bit Addressing Forms with the ModR/M Byte you can see that operand BL with a 16 bit displacement disp16 means a modrm byte of 1E followed by 16 bit displacement, so the complete instruction is 8A 1E 0A 00. You can verify that with an assembler:

8A1E0A00                mov bl, [10]

PS: It's unclear what offset you really want, but I trust you can fill in the correct one.

Upvotes: 5

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