Mike's PCjr Page

Minor suggestion: Add a 1x2 .1" header for HD activity LED (from the XT-IDE schematic). It would be nice to drill a small hole in the front end of the sidecar enclosure and hot-glue a dome LED with leads in the hole.

Never-mind!

They are not soldered. All 60 pins are friction locked in the rings. Had to push each one through with needle nose but got the connector apart.

Need some advice on connectors. I took the solder side shroud off a PCjr parallel port sidecar PCB. The pins didn't have solder on the rings on the top side of the board. So I figured it's on the underside. But without access, there's no way to wick it up with a braid or suck it out with vacuum. So ...

I started going down a CPLD route to sorta see what was possible. The only practical part choice (through hole / 5V / and still in production) is the Atmel ATF150x line. Unfortunately they are stingy with their synthesis license and even if I did get one it would only be a 6-month eval. So I'm stuck...

I would be shocked if that layout auto routes even @ 6/6 with only 2 layers. And if it did, you'd have more vias than pin holes. Your component placement looks a little scarey. Very simple changes would go along way there (eg. staggering the RAM/ROM pins, orienting the IDE data bus buffer and latche...

You are inverting the polarity of the signal. You either need to cascade another inverting NPN or use a discrete 7404 output on the base if one opens up (don't add another just for that). You also need to switch the R7/R4 resistance values. If layout makes adding it difficult, worry about it. That c...

With memory mapped IDE, it might be a good idea to tie the ready lines together - ideally with an NPN or darlington.

I see my mistake on the '138. You are indeed correct. As for chip selects, yes successive I/O IDE reads/writes would either hit different CS strobes on the IDE connector when doing word fetches or be interleaved with a memory access for the next instruction. That's changed now. Also you have the buf...

I think that '573 was only being used to provide enough drive current for those signals. I'm not sure why a '245 wasn't used initially. My only comment so far is it looks like the switches select one of 8 16KB windows between C0000 and DFFFF. 8KB of the flash is mapped in the lower half. The IDE reg...

Many PROM programmers will also do common PAL types (Rs, Ls, and Vs which are R+Ls). But to be sure you have to check with the manufacturer's specs. I got a surplus ChipMax 2 USB programmer relatively cheap that will do most. I'm not sure how the wait state generator on the Jr behaves. For 5150/60 a...