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program counter increment
http://www.easy68k.com/EASy68Kforum/viewtopic.php?f=5&t=1164
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Author:  PiCiJi [ Sun Feb 17, 2013 7:40 pm ]
Post subject:  program counter increment

Hi,

i have a few problems understanding which value the pc contains at any given time of execution.

Is the program counter incremented directly before or after a prefetch (instruction or extension word) ?

I am wondering because of instructions like dbcc. In the manual it says the pc contains the address of the instruction + 2 at the time when generating the new pc for branch.

Because of the prefetch cycle of the last instruction, the pc seems to increase directly before a prefetch. If so it means the first instruction after a reset doesn't increase the pc.

Author:  clive [ Mon Feb 18, 2013 7:34 pm ]
Post subject:  Re: program counter increment

After the micro/nano-code consumes the word?

By the time the PC addition portion of the pipeline executes the PC has advanced past the opcode word, ready to fetch the branch target word.

Author:  PiCiJi [ Mon Feb 18, 2013 9:00 pm ]
Post subject:  Re: program counter increment

I got information, that incrementing pc is handled in microcode and not hardwired to prefetch.

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