Atari PC1 ISA expansion adapter - J2 & J8 pinout

[oracle_jedi]

Yeah I know this is the ST/TT/Falcon forum, but this is also where the occasional Atari PC threads land.

 

Does anyone have a definitive guide to the J2 and J8 headers in the PC1?

 

A few years back Curt posted this information:

 

 

But I am pretty sure this pinout is wrong.

 

Bumzy developed an ISA expansion adapter some time back, but I don't recall him ever sharing a final schematic.  He did share this image which came from Curt, and which shows most of the expansion:

 

 

So from this, we can deduce that the pint out is in fact:

 

 

 

So here is my question to the experts on the forum.   One - does this look right to you?

 

And two - do the J2/J8 headers need any kind of buffering, diodes, resistors or whatever before they are connected to an 8-bit ISA expansion card such as an XT-IDE or a Adlib Sound card?

 

There are not many images of the actual PC1 ISA expansion adapter, but in this image there appears to be some resistors and a capacitor in the design, and I am concerned that I may damage the PC1 if I miss out a needed component.

 

 

 

 

 

[lp060]

Perhaps someone here can help? https://www.facebook.com/groups/1619945831452530/

Edited December 31, 2020 by lp060

[leech]

10 hours ago, lp060 said:

Perhaps someone here can help? https://www.facebook.com/groups/1619945831452530/

I have a PC4, and totally needed to join that group!

[jedie]

I found this topic: I also work on a PC1 XT-Adapter here: https://github.com/jedie/Atari-PC1-XT-Adapter and have similar questions about needed resistors and a capacitor... Anyone?

 

(I'm not on facebook)

 

EDIT: On http://www.ataripc.net/document-archive/ is the PDF: Atari PC ISA Bridge.pdf that contains some more information on page 3:

 

Don't know if there are any difference to the pictures from above...

Edited July 28, 2021 by jedie

[jedie]

btw.: Sergey's "ISA 8-Bit Backplane " has some "bypass capacitors" and optional "terminating resitors"...

 

 

[oracle_jedi]

An update on this.

 

As the schematics on ataripc.net show, the J8 connector was reversed in my diagram above.   The correct pin out is:

 

 

After experimenting with a number of possible designs, including just creating a PC1 to Tandy 1000 adapter and then piggy-backing off everything there, I eventually settled on this design:

 

 

It allows 2 ISA cards to be installed.  One sits underneath, foil side up, component side down, and the second card sits on top, foil side down, component side up.   Both cards have the "rear of the PC" facing toward the PC1's power supply.

 

This design allows the case lid to be installed, although the ability to reinstall the shield will depend on how tightly the wires are tucked and how proud the top card is.   I've been running it without the shield on.

 

I used an XT-IDE card.  A super compact one from Blue Lava systems.   It came with a 64MB CF card pre-installed with DOS 6.2 so that made life simple.   

 

And with that I've been playing with Windows 2, GEM 3/3 and several other larger games such as "The Secret of Monkey Island".   So far everything has been stable, but this is only a prototype and more work needs to be done.  @jedimatt42 has been helping me figure out some power issues so I am hoping to get all of that settled in the next week or two and then send, what I hope is the final version, in for fabrication.

 

Since the PC1 can support 3 floppy disks - A, B and C, the XT-IDE can conflict with floppy C.   The boot screen allows you to tap F8 to force the system to boot the CF card.   You can also still use F2 to force the PC1 to boot the first external floppy.   On my HxC2001 I ended up removing the jumper for "floppy B" so that it no longer responded to signals, and that allows the PC1 to boot the XT-IDE if no disk is in the drive, and without having to tap F8.

 

Here's a couple more pictures of me testing.  I've created an album with additional images if anyone is interested.

 

 

 

 

 

[jedie]

Absolutely great! ?

 

Can you provide your PCB layout files?

 

I have to time to finish my work here: https://github.com/jedie/Atari-PC1-XT-Adapter ?

[oracle_jedi]

4 hours ago, jedie said:

Absolutely great! ?

 

Can you provide your PCB layout files?

 

I have to time to finish my work here: https://github.com/jedie/Atari-PC1-XT-Adapter ?

 

Absolutely.  I will upload finished Gerber files to Atariage and/or Github when I get the designed finished.   As you can right now this prototype is +5V only and using a pig tail that splices into the floppy disk power.   The next design will be a bit more elegant.   I see your design uses the 5.25 inch peripheral power plug but changes the assignment of pins to accommodate -12V.   I am puzzling the same problem as the Ad Lib cards all need -12V, and the internal PSU doesn't supply that rail.

 

Hoping to get this finished within the next two weeks.

 

 

[tjlazer]

Man I would love to get one for my PC1!  What all is needed to get this running?

[oracle_jedi]

15 hours ago, tjlazer said:

Man I would love to get one for my PC1!  What all is needed to get this running?

 

Trying to get the final design finished this weekend.   I am going to use an LT1054CP to generate a -12V line, and use a 3.5 inch PC power plug, so you can drive it off the internal PSU, or an external one.

 

My PC1 has an Exxos power supply so I think I have enough grunt to drive two small cards.   If you have the original power supply you might want to consider powering the expansion adapter externally.

 

I am hoping to send this final design in for fabrication no later than Monday, so give it week to get back, and another to test, and hopefully if I don't screw anything else up, I can release the Gerber design then.

 

[oracle_jedi]

Hey everyone,

 

I got the PCBs back from JLCPCB finally - I managed to hit Chinese New Year apparently so that slowed everything down - and after a few days testing everything seems to be working pretty well.

 

I put together a short video showing the card and installing it in the PC1.

 

 

And then 

 

 

 

I've also put together a GitHub page with the Gerber and the Diptrace files:

 

https://github.com/oraclejedi/ATARIPC1_ISA

 

I have designed a few updates to the board and I sent them in to fabrication today.   The changes are:

 

Repositioning the bypass-caps so that they do not interfere with the expansion cards.

Adding pull up resistors to the MEMR, MEMW, IOR and IOW lines.  I don't know if I need these but I wanted to test this and see what difference they make - if any.

I also make the power traces larger in the next release.   This version seems stable but I am always looking to improve.

 

A few observations:

 

My PC1 seems to refuse to go into EGA mode on a cold boot.   I have to CTRL-ALT-DEL reboot the machine first, then EGA mode seems to work.   I only have a Commodore 1084 monitor so I am relying on games using the 640x200 EGA color mode.   

 

I am running BIOS 3.06 and I see that 3.07 had some updates to the video display code so maybe I should try an updated BIOS.

 

I have had this running for hours at a time without too many issues but I have experienced two complete 100% lockups - Leaderboard did it - and then Windows 2 also locked up.   I will continue to investigate this with the revised board designs, and the updated BIOS when I get around to that.

 

Below is a second video showing "The Secret of Monkey Island" and also "Prince of Persia" running on the PC1 with Adlib sound and running off the XT-IDE.

 

 

 

 

 

 

 

 

 

 

Edited February 20, 2022 by oracle_jedi
YT screwed up my video

[Paul Westphal]

Nice Work!

[jvas]

Wouldn't it be more convenient if there was a daughter board with more than one ISA connectors outside of the case and connected to the internal board with a ribbon cable?

[tjlazer]

Awesome!  How can I order one of these?  I would like to get one for my PC1.

Edited February 23, 2022 by tjlazer