HCS12 DBNE Instruction Timing

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HCS12 DBNE Instruction Timing

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GregYork
Contributor I

I am trying to understand the instruction timing listed in the HCS12 reference manual for the DBNE instruction.  Is this an instruction where 3 cycles are required if the branch is taken and only 1 cycle if the branch is not taken?  "PPP/PPO" would seem to indicate that this is not the case.

 

Thanks for any help someone can provide on this.

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pgo
Senior Contributor V

From the HCS12 CPU manual:

 

O —Optional program word fetch (P) if instruction is misaligned and has
an odd number of bytes of object code — otherwise, appears as
a free cycle (f); Page 2 prebyte treated as a separate 1-byte instruction

 

P —Program word fetch (always an aligned-word read)

 

The DBNE instruction will take 3 cycles whether the branch is taken or not.

 

I think only the normal branches have different executions times when the branch is taken/not taken.

(PPP/P)

 

bye

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