8086 opcode sheet

However, if you see something that doesn't look right, please contact me. To use the map, find the cell in the row labelled with the opcode's most significant 4 bits, and the column labelled with the opcode's least significant 4 bits. Both operands are of type "v", so both are WORDs.

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The instruction contains a relative offset to be added to the address of the subsequent instruction. Disassembly by hand Building the map lines of Python. I wanted to focus on integer opcodes in this map, as floating-point would be exceedingly rare in production code. If you're interested in reading more about the disassembler, the following posts might be worth a 8086 opcode sheet.

If it is a memory address, the address is computed 8086 opcode sheet a segment register and any of the sheeg values: This distinction only affects dis assembly, since the order of operands is irrelevant to TEST's function.

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Other special symbols can be looked up in the " Special Argument Codes " table. If you're interested in reading more about the disassembler, the following posts might be worth a look: GRP2 E v 1. This is an HTML-ized version of the opcode map for the processor.

The map is split in half; columns appear in the first partwhile columns 8-F appear in 8086 opcode sheet second. To use the map, find oopcode cell in the row labelled with the opcode's 8086 opcode sheet significant 4 bits, and the column labelled with the opcode's least significant 4 bits.

Note that arguments may be 8086 opcode sheet in both the opcode map and the opcode extensions table e. I want to use this map to build a disassembler, not a simulated processor, and the extra arguments would only be burdensome.

The operand value is encoded in subsequent bytes of the instruction. I wanted as simple a map as possible, and, to that end, this map contains some lacunae: A constant argument of 3, implicit sjeet the opcode, and not represented elsewhere in the instruction.

The 8086 opcode sheet remaining complexity involves "group" opcodes, such as Unusual in that arguments of this type are suppressed in ASM output when they 8086 opcode sheet the default value of 10 0xA.

I wanted as simple a map as possible, and, to that end, this map contains some lacunae:. Yes, with nearly 30 years hindsight, there probably shouldn't be an 8086 opcode sheet opcode devoted to this operation.

This map was constructed by taking a map for a more recent x86 processor and removing information irrelevant 8086 opcode sheet the much earlier processor. GRP2 E b 1. However, if you see something that doesn't look right, please contact me. To disassemble "group" opcodes, consult the " Opcode Extensions " table for any entry in the opcode map with a mneumonic of the form GRP.

Other values are illegal. In addition to the information that was removed, 8086 opcode sheet map contains two known errors.

This restriction is not shared with other opcodes with "E"-addressed arguments, and not reflected in the map. Arguments sehet either a pair of letters - the first in upper case, the second in lower case - or a special symbol. All the preceeding remarks about opcode 84 apply equally here. I wouldn't expect to see this in code as the "POP 8086 opcode sheet instruction is particularly useless and wanted to shret its appearance as an error condition. 8086 opcode sheet

Both operands are of type "v", so both are 8086 opcode sheet. As far as I know, this opcode map is, modulo the lacunae and errata mentioned above, correct. A constant argument of 1, implicit in the opcode, and not represented elsewhere in the instruction.

The operand is either a general-purpose register or a memory address. SI turns out to represent as one might expect the bit SI register, so opcode 4E simply decrements 8086 opcode sheet register by 1. Normally, however, the arguments from the opcode map are used.

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