Mike's PCjr Page

Haha yea I think if they had put a read/write toggle line in there it would've been a lot more flexible, but gotta play the cards we've been dealt :lol: . I suspect that for a co-processor that requires generally requires the same number or greater number of writes vs. reads, it probably makes more ...

It looks like there actually was a period clock chip (https://www.brutman.com/PCjr/pcjr_options.html#Integrity_Technology_Clock_Cartridge:) and it's (eventually) on my list to add as some more advanced Gameboy games (Pokemon Gold/Silver for example) has RTCs. Any software running on cartridge would ...

Howdy folks! As I've been reading up on the IBM PCJr (both the criticism of the day and modern looks at the system), it seems that the primary re-occurring theme of both then and now is a focus on the IBM PC: what it lacks in comparison to a PC, how to modify it to make it a somewhat useable PC, etc...

Haha nice! Definitely recommend using/looking at booterify over my dirty hack, booterify is way better (I find that writing my own tools is how I learn what the heck it's actually doing)! I did chuckle when I saw you had a function to implement the DOS print string interrupt because I ended up doing...

Has anyone written a small program to help calculate the CRC values for cartridges? I did briefly look for the routine in the BIOS and found it but am not familiar enough to determine exactly what it is doing, although I bet it's fairly basic. So the entry of interest is in the BIOS is: FFE71h (A-1...

I've been looking into it as I'm designing cartridges to fool around with, Tech Reference (Appendix A) has the full BIOS listing which is the primary source of truth. It's commented really well, though with 8088 ASM being a bit of a bear (in my opinion :lol: ) it can be tough. Cartridge headers diff...

That... :lol: oh goodness makes perfect sense, THANK YOU! I've played a decent amount with hardware interrupts on embedded platforms but really never dealt with SW interrupts as an API (which I think is a pretty neat design choice) so for some reason my brain refused to process the idea that an inte...

I haven't been able to find anything in the English text sections. I've read through various sections on the cartridges, diskette sections, BIOS programming, etc. with no luck on something disabling interrupts without re-enabling them (the disk IO stuff does seem to disable them but in theory it re-...

Sorry for the complications, I'm usually in the 3D printing mindset when I code where I'm juggling a bunch of experiments simultaneously to optimize my limited time but in this case I should've focused. I ran the simplified code example: MAIN: sti INF: jmp INF and as you both correctly predicted, th...

@Brutman + anyone mildly curious about it, So I wrote a test cartridge program to read MOTOR_COUNT(0000:0440) (or so I think, 8088 amateur here :lol: ) and save it to RAM at the very beginning, and it looks like by the time the BIOS gives my MAIN control via the int 18h call, the MOTOR_COUNT is alre...