8088/86 general instruction format doubt

[DEV123]

Hi friends,
Generally any opcode for 8088/86 is having a 6 bit field in instruction format. But 6 bits corresponds to 2^6 = 64 combinations and only max 64 instructions are possible. But already there are 117 instructions for 8086. How is it possible?

Can Anyone explain?

-Devanand T

 

[laurenrodriguez1]

I think you mean 'CISC' and 'RISC'. These refer to two ways of designing an instruction set for a computers processor or CPU. CISC is Complex Instruction Set Computer. This is how computers all used to be designed. This produced a complex chip. Early chips like Intel 8088/86 and Motorola 68000 were designed in this way.

RISC stands for Reduced Instruction Set Computer. On these chips, the instruction set is paired down to the absolute minimum needed, and complex operations are performed with multiple instructions.

 

[TonyM]

Can Anyone explain?

-Devanand T

The MCS-86 instruction format is more complicated than that. An instruction can have multiple extension bytes for more instruction encoding and/or operands, such as immediate data and addresses. I'm not an expert on it but have a look in the Intel 8086 data sheet near the back, it's all detailed there.

Look on http://datasheets.chipdb.org/Intel/x86/808x/datashts/8086/