Mike's PCjr Page

It seems that whenever I get bored, I go back to working on this.

I manually routed a one-sided PCB design for a 512k board today. It uses 11 jumper wires. The same design can be used to achieve 736k by piggybacking a 128k SRAM chip on top of the 512k chip and soldering another jumper wire for the 128k chip select. This design still requires a GAL16V8B or equivalent PLD and some means of programming it.

Alright, now I'm working on eliminating the jumper wires from my one-sided design. I got one of 'em out of the way, but I'd like to figure out how to get rid of more. This'll take some extremely clever and inefficient routing to get done.

Alright, I tried piggybacking a 128k chip onto my original 512k prototype. I tried three different methods of address decoding, but I just can't get jrconfig to recognize the extra RAM. I don't know if I should assume the RAM chip is bad, or what.

I feel terrible posting this so late, but keep going!

If you get it to a point where it's stable and you want to preserve it for posterity, we'll clean it up and put it on the web site as a modification. I need to be more active, but I've got too many irons in the fire already.

(My big thing is TCP/IP and Ethernet. At some point I need to graft a low-end Ethernet chipset onto the Jr. A multi-function sidecar with SRAM, Ethernet, an EPP parallel port and possibly IDE is the dream. I know the SRAM solutions work; Ethernet has been done for lesser computers. EPP parallel ports work, but chipsets might be hard to find. And a friend of mine has done IDE for the XT so the Jr isn't too far away.)

When you say the Jr isn't too far away (for an IDE adapter), any idea how far away that is? (I am not an engineer, but am willing to help where ever I can)

Thanks,

John

Brutman wrote: My big thing is TCP/IP and Ethernet. At some point I need to graft a low-end Ethernet chipset onto the Jr. A multi-function sidecar with SRAM, Ethernet, an EPP parallel port and possibly IDE is the dream. I know the SRAM solutions work; Ethernet has been done for lesser computers. EPP parallel ports work, but chipsets might be hard to find. And a friend of mine has done IDE for the XT so the Jr isn't too far away.

New thread...

I thought I'd post back here just to say, I'm sorry, but I'm not sure I'll ever get a procedure written up for this mod.

I do still intend to post a list of the points I tapped on the motherboard, though. I think that, and the schematic that was posted by someone else should be enough to get this mod done.

Well guys, I had to remove my RAM upgrade. The wires started getting tangled and a little bit unmanageable. Insulation was shrinking, and things were shorting out. It's not stable enough with that connection method to use beyond experimenting.

I'll start putting some more effort into getting a PCB plug-and-play version put together. The main problem I'm facing is that I don't know what I can use for a pass-through CPU socket.

When I was doing stuff on perf-board and needed a pass-through I'd always just get a string of header pins, cut them to size and wire them in parallel to the socket I was going to use. You had to solder 'tight' and trim them down to get the socket in place over one of the rows of pins (dremel to file them down and make a groove in the bottom of the socket helped), but it generally worked without fail.

Was a lot easier than trying to 'tap' a socket, solder pins to the bottom of where the socket is soldered, or get a socket with extra-long pins. Also ended up a bit more 'sturdy'.

I was thinking about trying to use one of these:

http://search.digikey.com/scripts/DkSea ... me=A136-ND

Seems like a similar idea to what you're describing.