Mike's PCjr Page

Anything ceramic and 10V or higher. I recommend using temp types X7R, X5R, or C0G/NP0.

The only time I was able to successfully boot 6.22 is when I completely replaced the first 128K visible to the CPU with off-board memory and gave all the 128K on-board exclusively to the video gate array. But this isn't easy to do and breaks all sorts of software including the JR's own video BIOS. Y...

Did any of that make any sense?

The short answer is 'sort of'. I've modified my board to remove the 2Kbit 24S18 decode ROM at ZM56 and replaced it with a 22V10 PAL. It has the responsibility of generating memory related chip-selects on 32K boundaries for the Video Gate Array (VGA), cartridge slots, side-car connector, and all of t...

I'm pretty sure there are no issues with Akbkuku's design as far as capacity. You'd have to check the data sheet of the PicoPSU you install to make sure it's per rail limits are not being exceeded. I'd imaging any ATX PSU has crazy high limits for 3.3V but it might have a significantly lower limit t...

alanh wrote:For example, 5% duty would be 14318181 - (75 * .05) Hz, where a 95% duty would be 14318181 + (75 * .95) Hz.

Just correcting my math:

5% duty would be 14318181 - (75 * 14.31 * .95) Hz (, where a 95% duty would be 14318181 + (75 * 14.31 * .95) Hz.

So 14317161 MHz (5%) to 14319212 MHz (95%)

What part of 'dead on balls accurate' is hard to understand? :) The cliff notes version is no local oscillator is 100.00000% accurate to the frequency printed on the can. You know this, hence the problem you are trying to solve with GPS. So get an oscillator with a +/- fine frequency adjustment. Cou...

You silly software engineers and your 'code'. The 'proper' way to solve this is with a VCXO and three numerical counters. With something like an FPGA (or even CPLD), the logic is simple. Building one out of discrete logic is possible though, and might be a fun challenge for someone. The idea is you ...

Has anyone ever run Minix, early Coherent or QNX, PC/IX, Venix, ELKS, or Idris on a Jr? They all supported generic 8086/8088 systems at one point. Though impossible to offer memory protection or demand paging, the segmentation scheme does act a bit like a rudimentary MMU for 16-bit relocatable virtu...

Just curious what the success rate has been with these on a Jr. I only have the PIC18 based SD card version. But I have not been able to get any image to boot - either 720K or 360K. I've tried 300 and 360 rpm for both with the standard 9 spt, 2 heads, 250 Kbps, and 40/80 tracks for 5.25/3.5 respecti...