问题
How many number of machine cycles are required for the RET instruction in 8085?
Why does it require that many number of cycles?
回答1:
The RET instruction needs 3 machine cycles. One to fetch and decode the instruction (4 T states), and two more machine cycles (that is, 2*3 = 6 T states) to read two bytes from the stack (stack is exterior to microprocessor, stack is in read-write memory, so to exchange data with stack needs machine cycles). Thus, the RET instruction needs a total of 3 machine cycles and 10 T-states.
Ref.: How many machine cycles are required for RET instruction in 8085 microprocessor is ? (sic).
回答2:
The RET instruction takes 10 cycles, according to the table at this site: http://www.cavehill.uwi.edu/fpas/cmp/online/el21c/lesson18.html
The instruction requires 3 memory fetches, one for the opcode and 2 for the return address, with each fetch taking 3 cycles (or more if the memory requires wait states). The opcode decode takes one cycle more.
来源：https://stackoverflow.com/questions/8127748/number-of-machine-cycles-required-for-ret-instruction-in-8085