Mike's PCjr Page

All of the problems I've listed are actually valid. I'm not making them up. You need to check again. I'm just trying to help. 1) Fixed. Your new address decode windows are now: 0x30x, 0x32x, 0x34x, and 0x36x. Though the chip selects will go active on memory accesses to that range during early boot u...

I must not have an updated schematic. Is V2 the latest? There's a ton of problems with it: 1) U5 has 2 floating inputs (R3 & R4). 2) I'm not sure why you have U6 pins R2, R3, and R5 pulled up and then shorted to GND. The pull-ups do nothing but waste power and require a second network that could...

Thanks for looking. 8288 bus controller de-multiplexes the bus control strobes from S0..2 when the 8088 is wired for maximum mode. I'm not sure way it never occurred to me that the Jr's CPU is probably in minimum mode since there isn't support for a 8237A DMA controller or 8087 math co-processor (th...

I'm a little confused. Are you doing this off the side car slot or a inline daughter board between the 8088 and the socket? You're schematic a few pages back seemed to indicate the later, but you're using the minimum mode pin assignments. Or does the PCJR actually not have an 8288 and use minimum mo...

It looks like there is enough room that if I put a 5 pin header on the board next to the card edge and removed part of the cartridge connector shroud on the MB where I could get to it, I could patch over IOR, IOW, CS, RST, and a ground from a small PCB sitting in the modem slot. Would make the idea ...

NM, I just realized there are no separate strobes for the cartridge address ranges since they are assumed always to be ROMs. I'm guessing the generated chip selects are only gated against memory read and not memory write. Disregard the above. Would have been nice though to have a jr with a front pan...

What about making a small PCB with an edge connector that fits in one of the front cartridge ports with a PIC32 and a USB type A connector. Maybe cut an existing cartridge case down a bit shorter so it doesn't stick out as far then size the PCB to fit. Since the ROM range decode logic is already on ...