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GARTHWILSON
PostPosted: Thu Aug 05, 2021 9:27 am 
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MichaelM wrote:
The PIC is naturally a 4 clock cycle machine. Running Phi2 into the clock input of the PIC is going to effectively force the PIC to operate at 1/4 the clock frequency of the 6502/65C02.

The PIC16's instruction cycle is 4 clock cycles.  The 65c02 also averages approximately 4 cycles per instruction, a little more or a little less depending on what you're doing; so they would be approximately equal except that the 65c02's richer instruction set lets it get the job done in about half as many instructions, according to my experience.  (I've brought a dozen products to market with PIC16's, but never used its PSP.)  A PIC16 running at 20MHz would not be less than half the speed of a 65c02 running at 20MHz.

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BigEd
PostPosted: Thu Aug 05, 2021 10:06 am 
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But I'd still agree with Michael: the PIC should be clocked fast. Especially for the difficult case, where a read request comes in and the PIC needs to do some work to get the right value into the output port before the end of the read cycle.

I do see hints that some PIC18F models have a PSP but haven't found a simple answer. It does seem that the PIC18Fs to hand lack the PSP.
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Jmstein7
PostPosted: Thu Aug 05, 2021 2:01 pm 
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BigEd wrote:
But I'd still agree with Michael: the PIC should be clocked fast. Especially for the difficult case, where a read request comes in and the PIC needs to do some work to get the right value into the output port before the end of the read cycle.

I do see hints that some PIC18F models have a PSP but haven't found a simple answer. It does seem that the PIC18Fs to hand lack the PSP.


PSP seems to be a "hidden feature" in a bunch of 18Fs, though I could easily be mistaken. They seem to have that capability, but it is not mentioned in the datasheet.

Again, I could be wrong.

-Jon
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Jmstein7
PostPosted: Fri Aug 06, 2021 1:56 pm 
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MichaelM wrote:
I too haven't used the PSP in a way more years than I'd like to remember.

I do wonder about connecting the PIC's clock input to the Phi2 clock of the 6502/65C02.


Michael,

Ditto, I had the same though - so, maybe I can use the PIC clock to drive PHI2? I'm using a WDC65c02S, so it can handle a little speed. Or, maybe I can drive the PIC at a "high speed" and send a 1/4 clock to PHI2?

-Jon
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GARTHWILSON
PostPosted: Fri Aug 06, 2021 7:22 pm 
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They can both handle 20MHz, and probably more, but I've never heard of any efforts to see how much more the PIC can handle above what it is spec'ed for.  It sounds like there's more margin on the '02 than there is on the PIC.  In any case, make sure you give the '02 a really clean clock signal with fast slew rates.

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Jmstein7
PostPosted: Fri Aug 06, 2021 7:31 pm 
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GARTHWILSON wrote:
They can both handle 20MHz, and probably more, but I've never heard of any efforts to see how much more the PIC can handle above what it is spec'ed for. It sounds like there's more margin on the '02 than there is on the PIC. In any case, make sure you give the '02 a really clean clock signal with fast slew rates.


Yeah. I’m going to have to use a good ‘scope for this one. I’ve suffered the plight of crappy signals too many times. Lots of wasted boards.

-Jon

PS thanks for the soldering tips; I’m fairly good at that now. I almost never use breadboards for anything but really basic tests, now.
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