Mike's PCjr Page

so... after 956 weeks of working at home.... hehe i've worked from my home office for a little over 18 years, so the covid stuff didn't really affect me work schedule much! for 2020 i had some fun PCjr projects! i did a replica of the 64k Display and Memory card! https://hackaday.io/project/172158-...

raphnet wrote:Yes those are perfect! Thank you so much for taking the time to take those pictures!

Thanks to these I was able to add a small section to my page where I try to learn what I can by following the tracks on the PCB.
https://www.raphnet.net/divers/pcjr_qui ... x_en.php#6

nice write up!

If you are interested in picking up a Hotshot II to check out for yourself I did spot this https://www.ebay.com/itm/Vintage-IBM-PCjr-Model-4860-Computer-with-jr-hotshot-ii-Untested-JRHOTSHOT/233643117847 dandy thanks! i'll bid on that! Brutman - if i win the bid on that, and write up some documenta...

It's not that simple. The 64K on the motherboard is directly wired to the video controller circuitry. So is the 64K in the memory card slot. On a 64K machine some of the advanced video modes are not available because the base 64K doesn't have enough bandwidth to satisfy the video controller. When t...

I have had an idea for a while, but not the knowledge to know if it will work or the skills to try. If you made an 128k static ram card for the memory slot, which should just require a jumper wire to connect to another address line, could you then disable ram refresh and have the lower 128k as fast...

So this is a drop-in replacement for the existing 64KB card? Does it have any advantages over the original card besides reduced part count and presumably lower power draw? I remember that PC Enterprises managed to cram 192KB onto their replacement card, but that required some additional wiring/moth...

So this is a drop-in replacement for the existing 64KB card? Does it have any advantages over the original card besides reduced part count and presumably lower power draw? I remember that PC Enterprises managed to cram 192KB onto their replacement card, but that required some additional wiring/moth...

Greetings All! just wanted to announce that my 64K Memory And Display Explansion replacement boards are up and running! the design is open source (non-commercial) and all the design files are available here: https://hackaday.io/project/172158-ibm-pcjr-64k-display-module 20200709_230745-small.jpg 202...

If you are interested in picking up a Hotshot II to check out for yourself I did spot this https://www.ebay.com/itm/Vintage-IBM-PCjr-Model-4860-Computer-with-jr-hotshot-ii-Untested-JRHOTSHOT/233643117847 dandy thanks! i'll bid on that! Brutman - if i win the bid on that, and write up some documenta...

I don't have a jrIDE myself, but what I would find interesting is: A scope trace of a data line, and an address line (either A0, A1, or A6). MEMR/W would also be mildly interesting, as those lines hit 4 devices in the jrIDE design (ROM, 2 RAM, and CPLD1) I'd like to see that, zoomed in a little, to...