Question

how to determine number of machine cycles for particular instructions in a microprocessor?

Answer 1

like for a instruction
LXI (load registor pair with 16 bit immediate data) has 3 macine cycles:and
they are =1 opcode fetch
and 2 memory read
i just want to know how i can say that it will have 1 opcode fetch and 2 mem.read or something else

Answer 2

@e.mccormick could use a little insight of yours :)

Answer 3

I never did Machine Organization, but I know it is partially processor dependent. Which instruction set you use determines how much each instruction costs. This is the whole CISC vs RISC instruction set argument. So I did a little searching and found some info on that topic. Hopefully it will get you started in the correct direction.

http://en.wikipedia.org/wiki/Instruction_set

Answer 4

ok thanks i'll check u out :) but do u know someone in OS who can help me with this ?

Answer 5

@wio @ganeshie8

Answer 6

your databus is 8bit ?

Answer 7

yeah i'm using 8085 its data bus is 8 bit

Answer 8

then its simple

Answer 9

ok :)

Answer 10

16bit address and 8bit data if i remember correctly right ?

Answer 11

yes perfect :)

Answer 12

Ok, so you want to load 16bit data from memory into internal registers

Answer 13

yes

Answer 14

opcode fetch is same for every instruction

Answer 15

yes i know its same ok :)

Answer 16

the next two memory read operations are part of the execution phase

Answer 17

you need two memory reads because your databus is 8bit and you want to load 16bit data

Answer 18

yes!! it was that easy ?

Answer 19

basically your memory is also organized in 8bits itself. you just save the 16bit data in two continuous 8bit locations

Answer 20

yeah clear now

Answer 21

i can draw the timing diagram now :)