Some questions about assembly a. What is the purpose of the PIC\'s W register? b

Question

Some questions about assembly a. What is the purpose of the PIC's W register? b. Are there any instructions that will read from one file register (f) and write back to a different file register address in one cycle? c. How about instructions that read and write to the same file register address in the same cycle? d. Why do some instructions take 2 cycles and others take one cycle? What is the key difference between those two classes of instructions? e. Every processor ever designed has a NOP instruction (to my knowledge). Why on earth include an instruction that does nothing? f. Loosely describe what happens when the processor executes a CALL instruction and then the subsequent RETURN instruction. Describe it at the level of the block diagram that is found on page 7 of the PIC manual linked on our website.

Explanation / Answer

A- The register w is the general purpose register , in which you can transfer any data. During arithematic operations also you can move data here for arithematic operations with some other data at another register.

B- The MOV instruction can be referenced here. This instruction read data from one register and write it to another.

C- I think we can not move data within same register.

D- The simple MOV PUSH etc instructions are 1 cycle as they only read data from one place to another place. But CALL BRA etc instructions are 2 cycle instructions as they have conditions like if then etc. They need to check in the second cycle if the condition was met or not.

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