# which bit specify the opcode , source , destination , and addressing mode ?

#### Parth86

##### Member
hello ,

I need help to understand how does instruction fetch , decode and execute

Code:
ORG 000
MOV A,#55H ;load immediate value 55H into reg. A
MOV R0,A  ; move the content of A into R0
END
CODE Memory
Code:
74 55 F8
Code:
ADDRESS                                          Value
0000= 0000000000000000           74= 01110100
0001= 0000000000000001           55= 01010101
0002= 0000000000000010           F8= 11111000
Processor read Byte from Program memory at the address indicate by program then it start to decode and execute the instruction

MOV A,#55= 01110100 01010101 double byte instruction
MOV R0, A = F8= 11111000 single byte instruction

suppose we have 8 wires that tell the other part of processor to activate or deactivate
suppose we have opcode 74= 01110100 ; that tell, Do mov Operation and activate Accumulator. here I don't understand how many wire tell that do mov operation , how many wire tell that activate Accumulator ?

74=01110100

I am reading 8051 instruction set I don't understand which bit specify the opcode , source , destination , and addressing mode ?

#### Parth86

##### Member
Look here: Infineon Instruction Decoder
And do it soon... before the whole Internet is just you asking this same question
I have stopped working. I will come back But I don't know exact time, there are many people who always encourage me, always try to help me even I post stupid post. and Some people make me feel useless , stupid.

#### Ian Rogers

##### User Extraordinaire
Forum Supporter
I have stopped working. I will come back But I don't know exact time, there are many people who always encourage me, always try to help me even I post stupid post. and Some people make me feel useless , stupid.
Don't think like that... You can't ask stupid question... I really wish I could help you more, but to do that I would have to learn it myself.... I find your posts interesting and there are one or two that do answer... Your topic is very low level stuff, Its very hard to design a processor core ( rather you than me )...

You have 89 views already, so there are many others waiting for the same answers... Some do not ask those questions and will be so glad that you do!!