How many Machine Cycles are there in Jump Statements of 8085?

Question

Which Machine Cycles are required for any Jump Statement in 8085 if the condition to be checked satisfies and for the case when it doesn't satisfy?

EDIT: I know the number. I want to know what are those Machine Cycles. The first one is Opcode Fetch, but the rest of them?

There should be an "instruction manual" explaining this. – sharptooth Sep 05 '13 at 06:52 — sharptooth, Sep 05 '13 at 06:52
Do you possibly have an 8085? – Jonathon Reinhart Sep 05 '13 at 06:53 — Jonathon Reinhart, Sep 05 '13 at 06:53
@JonathonReinhart Yes sir, I do. – Ozil Sep 05 '13 at 06:56 — Ozil, Sep 05 '13 at 06:56
@sharptooth The instruction manual doesn't explains this. – Ozil Sep 05 '13 at 06:56 — Ozil, Sep 05 '13 at 06:56

score 5 · Answer 1 · edited Nov 19 '13 at 06:02

5

When the J condition is not satisfied, the cycles are

Opcode fetch (4 T states)
Memory read (3 T states) of the lower byte specified, while simultaneously checking the flag condition.

If the condition isn't satisfied, the processor ends this instruction cycle after these 2 machine cycles and 4+3 = 7 T states.

edited Nov 19 '13 at 06:02

Pbk1303

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answered Nov 19 '13 at 04:47

Srijata Chakravorti

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Michael · Answer 2 · 2013-09-05T07:19:49.943

According to this instruction set reference, a conditional branch on the 8085 takes 9 T-states (2 M-cycles) if the branch isn't taken, and 18 T-states (5 M-cycles) if the branch is taken.

A T-state equals one clock cycle on the 8085 as far as I know. An M-cycle is made up of several (3 to 6) T-states. Examples of M-cycles are "Opcode Fetch" (which always is the first M-cycle of every instruction); "Memory Read" and "Memory Write".
You can read more about the 8085's states and cycles in this document.

peteykun · Answer 3 · 2013-11-10T06:28:59.073

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When it does satisfy the condition, the cycles on a 8085A are:

JNZ 9050H

Opcode Fetch
Memory Read: to get the lower order address byte
Memory Read: to get the higher order address byte

4+3+3 = 10 T-States in 3 machine cycles

I got here because I myself am in search of what the cycles are when the condition is not satisfied.

edited Nov 10 '13 at 06:28

answered Nov 10 '13 at 06:23

peteykun

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score 0 · Answer 4 · answered Nov 20 '16 at 05:06

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If the condition is satisfied 10T states, otherwise 7T states in case of conditional jump. In case of unconditional jump JMP its always 10T states

answered Nov 20 '16 at 05:06

user7184376

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Can you explain what's wrong with [Michael's existing answer to this question](http://stackoverflow.com/a/18630013/224132), which conflicts with yours? Are they for a different revision of the hardware, or is the manual he found incorrect? – Peter Cordes Nov 20 '16 at 05:34

score 0 · Answer 5 · edited Mar 30 '19 at 18:28

0

Let's take ' JNZ 16-bit address ' instruction as example. And following code for understanding :

INR B           // B=03 H 
JNZ C200 H

Here the condition will be true because register B is not zero. Hence 10 t-states.

If register B =00 H then the JNZ condition will be false as it is zero. Hence 7 t- states.

True: OF + MR + MR = 4 +3+3= 10 t states
False: OF + MR = 4+3 =7 t states

edited Mar 30 '19 at 18:28

Dmitry

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answered Mar 30 '19 at 18:09

feather fun

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How many Machine Cycles are there in Jump Statements of 8085?

5 Answers5