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PET 4016 Upgrade options?

daver2

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Ah,

You have the Universal 2 board.

See here for links Y and Z: http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/univ2/8032090-7.gif.

This is where they are on the schematic: http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/univ2/8032087-06.gif.

You need link Y made for 16K but (for 32K) you need to remove link Y and install link Z.

Basically, with link Y installed, the RAM is disabled when BA14 is HIGH. This defeats the object of the exercise to add a further 16K of DRAM!

These links are by chip UE1 (and the speaker).

Dave
 
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daver2

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That link is for the Universal - not the Universal 2. That's where I started, and then realised the OP has the Universal 2 board as the links in their photograph were different.

Dave
 

WimWalther

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Thanks very much, that seems to have worked.

IMG_20220709_103456982~2.jpg

So now I feel like asking why CBM didn't just mark jumpers Y & Z as "16K" &:"32K"..

But I'm sure there's a Very Good Reason.
 
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WimWalther

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I didn’t think it was correct when it was stated earlier that the PET would just autodetect the RAM but I wasn’t positive about the universal boards.
Now I wish you'd have said something, because I just spent time worrying that I'd botched the job and troubleshooting a non-issue.

Fwiw I was also dubious about the auto detection thing, but knowing next-to-nothing about PETs I wasn't in a position to question anything. Anyway, I need to run a full test of the new & old RAM before I move forward with the next steps.
 

Eudimorphodon

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Now I wish you'd have said something, because I just spent time worrying that I'd botched the job and troubleshooting a non-issue.

Yeah, I’m sorry I didn’t fact check that at the time. I was skeptical but I figured it was at least a possibility, since Commodore seems to have given up on punching holes in the boards by the universal board era, that maybe they just hardwired them and eliminated the option of hanging RAM off that internal bus connector.

(Without memory size jumpers the onboard socket decoding would otherwise interfere with that even if it wasn’t populated.)
 

daver2

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It's good when a plan comes together...

I am not sure why that link is actually there myself.

The BASIC ROMs do an autosize on power-up - so should detect 16K - even if the link is set for 32K and the second bank of RAM is not fitted.

I suppose the hardware engineer designed the machine like that and production fitted the links accordingly.

I suppose that with 16K of RAM fitted - and the links set for 16K - this does leave a 16K 'hole' for something else. However, if the 'something else' still appears as memory at $4000 and upwards, BASIC will still carry on and treat it like memory. In this case, the link would still be superfluous - apart from the fact that something else could occupy the 'hole'...

Dave
 

Hutch

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My bad. I thought it would auto detect. I know with 32K it tests ram at startup and if you have a bad bit in high memory it will report 16K, so what's the point of even having jumpers.
 

Eudimorphodon

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… looking at the schematic the reason the jumper is needed is to (not) suppress the data buffers at UB9/10 if the motherboard RAM is selected. Without it then it’d be impossible to hang an external memory off the bus because the bottom 32k of address space would be locked out, regardless of whether it was populated.
 

WimWalther

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… Without it then it’d be impossible to hang an external memory off the bus because the bottom 32k of address space would be locked out, regardless of whether it was populated.
Is there any provision for installing this external memory? Did CBM foresee this possibility?

I mean to say that PETs (or at least my 4016) don't have an expansion / cartridge port as with the VIC & later machines. About the only way to connect it would be to literally wedge it in between the 6502 & socket.

That said, I should probably ask about those two dual male (40 pin?) headers on the right, rear of the board - what are they used for?
 

WimWalther

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Well guys, the machine passed what's passing as a full memory test. The test checks that each byte can hold 0 and 255.. and passes that byte if so.
 

WimWalther

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Quick question about the keyboard..

Are the little dark gray pads (on the tip of the plungers) sufficiently conductive as-is that they only need cleaning? Or should I try to embed a bit of powdered graphite into them to restore keyboard reliability?
 

Hutch

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Is there any provision for installing this external memory? Did CBM foresee this possibility?

I mean to say that PETs (or at least my 4016) don't have an expansion / cartridge port as with the VIC & later machines. About the only way to connect it would be to literally wedge it in between the 6502 & socket.

That said, I should probably ask about those two dual male (40 pin?) headers on the right, rear of the board - what are they used for?
These are the expansion bus connectors. Ram expanders and other devices all connect here and the boards stack above the mainboard on standoffs. Example

1657408788641.png
 

WimWalther

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Remember that I have no experience with PETs.. But I found something that seems odd.

If I POKE 59468,14 it shifts to the alt (lowercase) character set as expected. But if I ?CHR$(14) it also shifts to the alt set, but something else happens. It's like the monitor refresh rate or overscan changes. The raster briefly hiccups and then stretches out so the text runs over the vertical borders, or at least the upper border. I've never seen this on a VIC or 64, fwiw.

What's going on?
 

Eudimorphodon

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These are the expansion bus connectors. Ram expanders and other devices all connect here and the boards stack above the mainboard on standoffs. Example

View attachment 1243413

Yes, this. Way back in the thread I mentioned that cobbling together a simple board to stick on these headers would be an alternative to the CPU socket or PCB surgery if your machine did have a "hole-y" motherboard.
 

Eudimorphodon

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What's going on?

When you use the control code the CRTC is being reprogrammed to add an extra blank line between character rows in lowercase mode. (Which as you've noticed can mess things up a little if your monitor's overscan is set up to fully fill the screen in graphics mode.)

The reason for this is Commodore decided that the extra line for descenders made lowercase more readable, and with the CRTC it was "free", or nearly so, to implement.
 

daver2

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No key combination, but there is a POKE to switch in (or out) the other 'half' of the character generator.

It just eludes me at the moment, but a bit of searching should identify it.

Dave
 
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