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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 15th Aug 2023, 5:28 pm   #681
ajgriff
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Default Re: Commodore PET 4032/8050/3022

Just to confirm that the W65C21N and MC6821 PIAs work perfectly in my 2001-8. At the time the W65C21N was easy to find but that no longer seems to be the case as Colin has discovered.

Alan
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Old 15th Aug 2023, 5:30 pm   #682
SiriusHardware
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Default Re: Commodore PET 4032/8050/3022

You've already found some but for future reference I found an old repair thread by Tynemouth Software saying that the 65C22 is also, as might be expected, a usable replacement for the original 6522 in PETs.

Yep, AJ, the W65C21Ns seem to have disappeared off the face of the earth, I should have looked myself before sending Colin off to look for them. Maybe a Commodore user group somewhere hoovered up the entire stock and is hoarding them all.
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Old 15th Aug 2023, 5:33 pm   #683
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Default Re: Commodore PET 4032/8050/3022

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Originally Posted by SiriusHardware View Post
What exactly is the difference between the 6520 and the 6521, does anyone know? I can't fathom the logic(!) of making functionally identical ICs with side by side numbers, although on rare occasions there is the realisation that a well known / well used chip has some weakness or bug, so a 'MK2' version gets made which has a slightly different IC number, but is presented as a better alternative to the original. Presumably that is what has happened here?
Does this help?

https://www.westerndesigncenter.com/...placements.php

Alan
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Old 15th Aug 2023, 5:38 pm   #684
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Default Re: Commodore PET 4032/8050/3022

It doesn't really explain why there are legacy 6520 and 6521 chips with no apparent difference between them, but it is interesting to note that so many ICs are pin compatible in this role including the Hitachi HD6321 which wouldn't be an obvious one to think of.
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Old 15th Aug 2023, 5:49 pm   #685
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Default Re: Commodore PET 4032/8050/3022

Here's a tech note from Commodore showing the differences between the MC6821 and the 6520 fyi.

http://archive.6502.org/datasheets/c...821_mc6821.pdf

Colin.

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Originally Posted by SiriusHardware View Post
It doesn't really explain why there are legacy 6520 and 6521 chips with no apparent difference between them, but it is interesting to note that so many ICs are pin compatible in this role including the Hitachi HD6321 which wouldn't be an obvious one to think of.
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Old 15th Aug 2023, 6:02 pm   #686
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Default Re: Commodore PET 4032/8050/3022

Good find, so it looks as though the 6821 has a couple of tweaks which make it slightly superior to the 6520, although the article seems to be arguing the other way around, that it is OK to use the 6520 as a 6821 substitute as long as you don't need the tweaks.

Last edited by SiriusHardware; 15th Aug 2023 at 6:16 pm.
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Old 15th Aug 2023, 6:15 pm   #687
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Default Re: Commodore PET 4032/8050/3022

Tested a couple of spare 6821's in my 6800 system, the 6821 runs the keypad and display, it does a lot of I/O swapping so its a good test. Both perfick, will be northbound 1st thing tomorrow
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Old 16th Aug 2023, 10:16 am   #688
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Default Re: Commodore PET 4032/8050/3022

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It doesn't really explain why there are legacy 6520 and 6521 chips with no apparent difference between them, but it is interesting to note that so many ICs are pin compatible in this role including the Hitachi HD6321 which wouldn't be an obvious one to think of.
Well it seems that Motorola produced the MC6821 PIA with some slight differences / enhancements to the (MOS? original?) 6520.

Then producers of the the 65xx series responded by making their own version of the 68(21), and producing the 65(21).
So you would expect the 6521 to be slightly-different in some way to the 6520.

Although manufacturers have been known to sell exactly the same product, marked with different types numbers (often the alternative number matching a competitors one, to provide an alternative source).
TI do some 74LVCxxx devices as a different 74(VHC?)series, that rivals use, even issuing a separate datasheet for both. But comparing TI's spec's, everything is actually identical!


Hitachi did many (less common) HD63xx versions of 68xx IC's - with maybe some officially licensed clones, or enhanced alternaives.
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Old 16th Aug 2023, 10:56 am   #689
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Default Re: Commodore PET 4032/8050/3022

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There are a couple of pages about Superchip starting at page 12 of this (user group) newsletter. This repeats the statement found in the text file on zimmers, that superchip is intended to work in conjunction with 'Toolkit' which might be what is supposed to be in that other EPROM.

http://archive.6502.org/publications...1_jan_1981.pdf

That whole series of newsletters could be very interesting to read if they are all archived there.
From a quick Google, I did also find some reviews of the PET Superchip in Compute! Dec 1981 Issue19 (Page 158/159), that somebody had extracted these 2pages and uploaded / Printout Christmas 1980 (pages 23/24 + advert for it on page 34)
These / the Supersoft (Middlesex) advert (Where they also sell the Tookit at a reduced price) say the Superchip "gives owners of standard 40 column PET's many of the features of the new 8032 SuperPET - and much more besides. Single-key entry, auto-repeat are popular features, but the advanced programmer will find the User Definable FunctionKeys innovative and invaluable. Fully compatible with the Programmer's Toolkit'

I also read it provides scrollable 'Windows' areas of the display, that the 80-col Basic 4.0 PET had.

Looking in the readout's that Colin uploaded, I see it says Superchip 4000 at the end. So seems to be a different version to the 9000 one on Zimmers (Which also has quite a few unknown / possibly-corrupt images, so I wonder if these could be added to their collection case they prove useful).
Although maybe the Quick Ref Char / .txt file instrucyions on zimmers does apply to both (Although Sys call address may vary)
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Old 16th Aug 2023, 12:41 pm   #690
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Default Re: Commodore PET 4032/8050/3022

The '9000' in the filenames of the ones on zimmers refers to the base address of the location in which it should be installed, which in the 4032 would be UD12. The '4000' in the text 'splash screen' near the end of the file seems to refer to the version / revision name because (address) 4000 falls squarely within the RAM area, therefore the 4000 can't be a reference to the base address at which it is meant to reside.

I think that text at the end of the file probably gets displayed on the screen when you activate the EPROM by doing a SYS call to it.

I don't know if there would be any value in adding the code from Colin's EPROM to zimmers without knowing whether the code is intact or not.

Recently, we had a case in another thread where an EPROM worked in the target hardware but could not be read in the conventional manner by EPROM programmers. Maybe we have a reverse case here, where the EPROM is readable in programmers but not by the target hardware.

Colin was already going to try one of the Superchip images from zimmers, but it might also be interesting to try programming another chip with the code read from his original superchip EPROM to see if it causes the same behaviour when fitted.
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Old 16th Aug 2023, 9:37 pm   #691
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Default Re: Commodore PET 4032/8050/3022

Today's task was to rub down the black base of the case and spray it gloss black, pop on the new label and finally put everything back together.

I may remove the white US12 socket to try the Superchip EPROM - you never know.

But I'll play with it a little first.....

Here's both the PETs you helped me with - thanks very much. Another thing I want to try is the only multi-player PET game I know here:

https://portcommodore.com/dokuwiki/d...h_attack:start

Colin.
Attached Files
File Type: zip PXL_20230816_201701248.zip (2.07 MB, 34 views)
File Type: zip PXL_20230816_203204893.zip (3.78 MB, 38 views)
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Old 16th Aug 2023, 10:33 pm   #692
SiriusHardware
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Default Re: Commodore PET 4032/8050/3022

Yes, what's the point of fixing them up if you can't play with them afterwards? With no serial port as standard, I wonder how they talk to each other - via the IEEE ports maybe?

Edit: No, User Port to User Port: Here's the detail of the cable required.

https://www.youtube.com/watch?v=nNp9yu7l4Rk

Great to see them both on at the same time, I guess the 6821s arrived very swiftly from Phil. The new one is already looking a lot smarter.

That two player / two machine game sounds great!

Last edited by SiriusHardware; 16th Aug 2023 at 10:57 pm.
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Old 18th Aug 2023, 1:12 pm   #693
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Default Re: Commodore PET 4032/8050/3022

For the record, Phil__G was kind enough to send me 2 x MC6821 as a replacement for my 6520s; they work fine in the 4032 and all PIA controlled devices function correctly, so they are pin compatible in case anyone wanted an easier to find replacement for a 6520.

Colin.
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Old 18th Aug 2023, 2:51 pm   #694
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Default Re: Commodore PET 4032/8050/3022

We love it when a plan comes together
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Old 5th Oct 2023, 2:07 pm   #695
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Default Re: Commodore PET 4032/8050/3022

A quick update on the Superchip ROM that I had removed; I popped it into UD 12 to see I could coax it into action and by using the SYS command listed here:

http://www.zimmers.net/anonftp/pub/c...ip-toolkit.txt

It sprang straight into action and reports itself as SUPERCHIP4000 and works fine.

I'm in touch over email with the original author in an attempt to get a manual if possible as I can't find one out there on the internet (only a coupe of pages of it) and will report anything I hear back.

I believe this version may not be the one on Zimmers so I will get in touch with them and send them the .bin file for them to host if they wish.

Colin.
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Old 5th Oct 2023, 2:41 pm   #696
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Default Re: Commodore PET 4032/8050/3022

As you've now succeeded in getting that one to run I would say it's definitely worth adding your version to the range available from zimmers (if they want it, of course - I'm sure they will). It will be a great help for anyone wanting to check a suspect EPROM against known working code.

A few posts back you said that putting the Superchip EPROM back in was stopping the machine from working - was that down to another case of white socket disease?
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Old 5th Oct 2023, 2:55 pm   #697
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Default Re: Commodore PET 4032/8050/3022

The white socket is dodgy - sometimes when I type the SYS command it drops to the monitor and a gentle wiggle of the ROM sorts that out.

In another bit of news, I've discovered that the other ROM is another toolkit which also works fine - specifically the Palo Alto Programmers Toolkit referenced here although mine has a copyright 1980 message:

http://www.zimmers.net/anonftp/pub/c...olkit-b000.txt

Colin.
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Old 5th Oct 2023, 2:59 pm   #698
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Default Re: Commodore PET 4032/8050/3022

The document you linked to in #696 did seem to suggest that those two utilities were often installed as a pair, so it's good that it did prove to be the case.

What exactly does the Palo Alto toolkit do, any idea?
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Old 5th Oct 2023, 3:32 pm   #699
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Default Re: Commodore PET 4032/8050/3022

Ah, having read further I see that it is the well known 'programmer's toolkit' presumably supplied packaged as an EPROM by that Palo Alto outfit.
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Old 3rd Nov 2023, 12:33 pm   #700
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Default Re: Commodore PET 4032/8050/3022

One last question concerning the original repairs to this PET - at one point a 'proper' 6545 CRTC IC was ordered in case the UM6845 wasn't as compatible as hoped, although it did turn out to work well - did the 6545 ever eventually arrive and get put into the machine?
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