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VERA and the Colour PET


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8BG’s videos get me thinking about Commodore hardware specifically and 6502 hardware generally.  I think the form factor of the PET is one of the most visually appealing of the single-piece computers (along with the TRS-80 model 3). There’s something about them that screams “I must be taken seriously!”, whereas my Commodore 64 — which I loved — put on no airs, saying simply “I’m a superior game computer!”

 

So yesterday I one again read Steve Gray’s webpage on the Colour PET — a PET which repurposed its second set of video RAM as color RAM.

As a refresher: the PET had space for a parallel 1K bank of video RAM.  When enabled, the PET was in 80-column mode. ( In my mind, this was a landmark separating business machines from home computers. )  A little effort by Steve lets it serve color when in 40 col mode.

 

*Now*, however, I think the PET looks timeless, and so I “want” it to be *more* capable than it was. I’m an 80 column “snob”.  And I’m also a color snob, although the basic Color RAM seems enough for me.  And... I’m also a hardware sprite snob, because the C64 showed me how fun they are.  It’s taking time to warm up to VERA’s more complex sprites, but I now see exactly why multicolor mode is so nice.

 

And so I am thinking that VERA could turn any PET into a Color PET.  If so, then I think VERA is a very good thing.

Edited by rje
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The biggest issue, aside from determining exactly how to interface VERA to the PET's motherboard (which in turn raises the questions of exactly which sub-model of PET and exactly what sort of monitor it currently has), is that the 6502 used in the PET has a stock clock speed no more than 1/8 that of the 65C02 in the Commander X16.

Software written for the PET with a VERA on the motherboard has to to take this into account.  Otherwise, there could be frame rate issues...

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21 hours ago, Kalvan said:

The biggest issue, aside from determining exactly how to interface VERA to the PET's motherboard (which in turn raises the questions of exactly which sub-model of PET and exactly what sort of monitor it currently has), is that the 6502 used in the PET has a stock clock speed no more than 1/8 that of the 65C02 in the Commander X16.

Software written for the PET with a VERA on the motherboard has to to take this into account.  Otherwise, there could be frame rate issues...

You’d have to jack in to the system bus. This probably means a CPU wedge, like a lot of the Amiga expansions use. This is basically just a PCB that plugs in to the CPU socket - you’d then plug the 6502 into the VERA board.

The board would have to be a little more “active” than VERA and provide its own latches to handle VERA I/O, which means that you could probably use jumpers to set which model of PET is being used (putting VERA in that PET’s I/O space.)

Also, since the PET has its own video chip, you’d have to route the output from that chip through the VERA board. I’d assume you’d have some sort of relay to switch between the PET video and the VERA video when VERA is in use. 

Of course, if you customized the PET KERNAL, you could dispense with the default video chip entirely, by re-writing the video I/O routines to send output to the VERA board… but at that point, you’ve basically just turned the PET into a 1MHz Commander. 

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On 9/20/2021 at 5:32 PM, Kalvan said:

The biggest issue, aside from determining exactly how to interface VERA to the PET's motherboard (which in turn raises the questions of exactly which sub-model of PET and exactly what sort of monitor it currently has), is that the 6502 used in the PET has a stock clock speed no more than 1/8 that of the 65C02 in the Commander X16.

Software written for the PET with a VERA on the motherboard has to to take this into account.  Otherwise, there could be frame rate issues...

Yes, just as software written for a C64 with a VERA cartridge would have to take the slower CPU clock into account ... you cannot do as much at 1MHz as you can at 8MHz.

A universal Userport interface would be even slower, as you need to transfer data a nybble at a time.

Register Address Write mode: Set all to output, Write 000aaaaa, Write 100aaaaa, address bits are latched.
Port Write Low Nybble: Set all to output, Write 0010dddd, Write 1010dddd,
Port Write High Nybble: Set all to output, Write 0011dddd, Write 1011dddd
Port Read Low Nybble: Set high four to output, low four to input, Write 0110xxxx, Write 1110xxxx, Read xxxxdddd
Port Read High Nybble: Set high four to output, low four to input, Write 0111xxxx, Write 1111xxxx Read xxxxdddd

 

Edited by BruceMcF
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11 minutes ago, rje said:

So in other words, I'm better off figuring out how to get an X16 and its monitor to fit into a PET frame.  XD

I'll just say that if I had a PET chassis, I'd totally build a MiSTer or Pi based emulation system inside. Maybe even both, because why not?

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Except the MiniPet is ‘opaque’ when it comes to the video circuitry.

Said another way, it uses an ATMega (I believe) microcontroller to render a composite signal (or Pet Monitor output) from memory.

Maybe you can consider the MiniPet disposable versus trashing a beloved vintage Pet and that is what you are suggesting.

I have both and can easily be convinced to hack into my homebuilt MiniPet. FWIW, the  video clocking of the MiniPet is semi-lame; the image is not centered on the screen and the developer has hinted at, but made no effort to correct the timing (if you have horizontal adj on your monitor it’s no big deal).  It works well with an ‘external’ monitor, however, and they helped me interface an old Kaypro CRT which I bought off eBay.  So I can’t complain about that.

My favorite part in that 8BG video above is his dreadful soldering skills.  I swear he does it for comedic affect.  “3 tools... Dremel, duct tape, sledge hammer”.  I think Kevin has been tutoring him, he did much better in the recent Apple I vid.

 

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4 hours ago, EMwhite said:

My favorite part in that 8BG video above is his dreadful soldering skills

he freely admits his soldering skills aren't that great. He probably does a better job than I do... but I do manage to get the job done, usually.

4 hours ago, EMwhite said:

Except the MiniPet is ‘opaque’ when it comes to the video circuitry.

The only reason I haven't bought a Mini-Pet yet is that it's based on the 40 column model. I really want an 80 column system...

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If I ever go off the deep end and actually become a true tinkerer I'd bid on something like this and, perhaps, gut it -- assuming it has multiple problems (mainboard, power supply, keyboard, monitor, who knows).  The case is in good shape.

https://www.ebay.com/itm/115005318802?hash=item1ac6d9e692:g:K7MAAOSwTPNhS9Td

Or, more perversely, a TRS-80 Model 4 case... $75...

https://www.ebay.com/itm/194385725279?hash=item2d424ac75f:g:AnYAAOSwqp5hTJDi

Edited by rje
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4 hours ago, rje said:

If I ever go off the deep end and actually become a true tinkerer I'd bid on something like this and, perhaps, gut it -- assuming it has multiple problems (mainboard, power supply, keyboard, monitor, who knows).  The case is in good shape.

https://www.ebay.com/itm/115005318802?hash=item1ac6d9e692:g:K7MAAOSwTPNhS9Td

Or, more perversely, a TRS-80 Model 4 case... $75...

https://www.ebay.com/itm/194385725279?hash=item2d424ac75f:g:AnYAAOSwqp5hTJDi

The "empty vintage" case I want is still the Kaypro II... but I passed on the last one I saw, and now I wish I'd bought it.

 

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On 9/23/2021 at 12:31 PM, rje said:

If I ever go off the deep end and actually become a true tinkerer I'd bid on something like this and, perhaps, gut it -- assuming it has multiple problems (mainboard, power supply, keyboard, monitor, who knows).  The case is in good shape.

https://www.ebay.com/itm/115005318802?hash=item1ac6d9e692:g:K7MAAOSwTPNhS9Td

Or, more perversely, a TRS-80 Model 4 case... $75...

https://www.ebay.com/itm/194385725279?hash=item2d424ac75f:g:AnYAAOSwqp5hTJDi

I have a Model III case and a page-white VGA monitor of the right dimensions to fit in it. They’ve been sitting around the house for the better part of two decades and I still haven’t done anything with them. 

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