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PostPosted: Tue Aug 03, 2021 7:45 pm 
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Hi, all - hope everyone is having a good summer (in the Northern Hemisphere). Here is a question for the experts:

if one wants to interface a 65c02 to the PSP of a PIC microcontroller, must he use a VIA or PIA (or the like) between the PIC and the 65c02's bus?

Breaking out /RWB into separate /read and /write seems simple enough, or does the connection require more? The PIC does provide a latch for the data. Finally, does anyone know of any code repositories out there for this purpose (addressing the PIC via the PSP)? I'm hardwiring all this to veroboard, so I need to get all the hardware right.

Thanks!

Jon


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PostPosted: Wed Aug 04, 2021 3:16 pm 
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Nobody knows the answer, here?


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PostPosted: Wed Aug 04, 2021 3:32 pm 
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I don't have knowledge of this, but... the PSP appears to be a bidirectional 8 bit port, with internal latches, and inputs for read, write and chip select. In other words, it allows the PIC to be addressed as a single location I/O device. As such, yes, it should be possible to connect directly to the 6502 bus, provided you have a bit of glue logic.
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PostPosted: Wed Aug 04, 2021 3:50 pm 
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Ed, thanks! This is my first time experimenting with PIC microcontrollers. -Jon


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PostPosted: Wed Aug 04, 2021 3:53 pm 
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Do let us know how you get on!


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PostPosted: Wed Aug 04, 2021 5:08 pm 
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BigEd wrote:
Do let us know how you get on!

Indeed, will do!


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PostPosted: Wed Aug 04, 2021 7:20 pm 
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PS I do have newer, "better" chips (e.g., the PIC18F45K40, etc.) - I just wish I knew how to create a PSP (effectively) on those. I also have a few 18F46Q84s around. I just wish I had a better handle on using them.

-Jon


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PostPosted: Wed Aug 04, 2021 7:51 pm 
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Pages 8 and on of this PDF might be indicative of some possible tactics
https://owd.tcnj.edu/~hernande/ELC343/Chapter_07.pdf


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PostPosted: Wed Aug 04, 2021 8:55 pm 
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BigEd wrote:
Pages 8 and on of this PDF might be indicative of some possible tactics
https://owd.tcnj.edu/~hernande/ELC343/Chapter_07.pdf

Ed, this is great information - thank you!!! -Jon


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PostPosted: Wed Aug 04, 2021 9:04 pm 
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Another relevant Microchip ap. note is AN579, about using the PSP, is at http://ww1.microchip.com/downloads/en/A ... 00579b.pdf .

I haven't looked that closely at the PIC18's, but many of the PIC16's have a PSP, parallel slave port, and I suspect the PIC18's aren't much different in that regard.  You can put it right on the processor's data bus, but it's slower than something like a 6522 because you have to for example write the data to the PIC, then give it enough time to see it and do something with that info, then come back again and tell it what it's supposed to do with that data, then again give it more time to process it, maybe polling it in between to see when it's ready for the next thing, and so on.  If you want to read data, you'll tell it what you want to read, give it time to get that data ready to output, come back later to read it, etc..  For this reason, it would be better to use the PSP only if the amount of data is rather small compared to the job the PIC will be doing with it.

I've posted this before and someone replied that newer PIC versions make it less cumbersome.  I can't find it right now.

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?


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PostPosted: Wed Aug 04, 2021 10:35 pm 
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GARTHWILSON wrote:
Another relevant Microchip ap. note is AN579, about using the PSP, is at http://ww1.microchip.com/downloads/en/A ... 00579b.pdf .

I haven't looked that closely at the PIC18's, but many of the PIC16's have a PSP, parallel slave port, and I suspect the PIC18's aren't much different in that regard.

...

I've posted this before and someone replied that newer PIC versions make it less cumbersome. I can't find it right now.


You are 100% right, Garth - precisely why I'm using the 18F-K... speed. And, of course, the more robust feature set. However, for the purposes of testing everything, I'm just going to see if I can't get an I2C 16x2 LCD up and running via the MPU. Just for testing, though. If I can get that up and running (and I haven't figured out how to do it yet), then I should pretty much be able to interface with the more useful features.

Jon


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PostPosted: Wed Aug 04, 2021 11:39 pm 
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Jmstein7 wrote:
I'm just going to see if I can't get an I2C 16x2 LCD up and running via the MPU. Just for testing, though. If I can get that up and running (and I haven't figured out how to do it yet), then I should pretty much be able to interface with the more useful features.

I have working I²C VIA bit-bang code, in various forms, at http://wilsonminesco.com/6502primer/GENRLI2C.ASM, to go with the I²C circuit in the 6502 primer's circuit potpourri page at http://wilsonminesco.com/6502primer/pot ... ITBANG_I2C .

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?


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PostPosted: Thu Aug 05, 2021 2:24 am 
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GARTHWILSON wrote:
Another relevant Microchip ap. note is AN579, about using the PSP, is at http://ww1.microchip.com/downloads/en/A ... 00579b.pdf .

I haven't looked that closely at the PIC18's, but many of the PIC16's have a PSP, parallel slave port, and I suspect the PIC18's aren't much different in that regard. You can put it right on the processor's data bus, but it's slower than something like a 6522 because you have to for example write the data to the PIC, then give it enough time to see it and do something with that info, then come back again and tell it what it's supposed to do with that data, then again give it more time to process it, maybe polling it in between to see when it's ready for the next thing, and so on. If you want to read data, you'll tell it what you want to read, give it time to get that data ready to output, come back later to read it, etc.. For this reason, it would be better to use the PSP only if the amount of data is rather small compared to the job the PIC will be doing with it[...]


Garth,

Question - when you put the PIC directly on the 'c02 data bus, do you need to connect the PIC to PHI2, or do you just keep using the internal oscillator in the MCU?

-Jon


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PostPosted: Thu Aug 05, 2021 4:38 am 
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Jmstein7 wrote:
Garth,

Question - when you put the PIC directly on the 'c02 data bus, do you need to connect the PIC to PHI2, or do you just keep using the internal oscillator in the MCU?

I've only looked at the data sheet and ap. note, and not recently.  I have not actually implemented it so far.  I expect you could run Φ2 into the PIC's OSC1 input, just to save parts.  It will use the PSP's RD\, WR\, and CS\ pins though, not coordinate transfers via Φ2 like the '22 VIA would.

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?


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PostPosted: Thu Aug 05, 2021 9:18 am 
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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.

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.

My initial recommendation would be to run the PIC with a dedicated clock, at or above, its maximum operating frequency, which is somewhere in the vicinity of 20 MHz. I expect that the PSP is designed to provide an interface to an external host that is operating asynchronously to the PIC. Because of this, the circuitry of the PIC's PSP should be capable of receiving data from a processor like the 6502/65C02 which is operating at a frequency that is not an integer multiple of the PIC's clock frequency.

As previously stated, there's a lot of work that the PIC's SW has to perform to make the PSP sing. Thus, my first thought is toward making the interface as efficient and fast as possible would be to run the PIC as fast as your selected component allows.

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