Re-execute Programs in Memory on CP/M

[@alexandermirdzveli3200]

Nice trick! There's a certain charm to simple systems.

[@snarfusmaximus]

My Cromemco Z-1 has a front panel with switches and LEDs. My favourite program for formatting floppies is Cromemco INIT which runs under CDOS (CP/M 1.4 like OS) but terminates after formatting just one disk. When I want to format multiple disks I halt the CPU via the panel, enter address 100H via the switches and examine location. The panel is effectively sending a JMP instruction to the CPU to do this. When I hit the run switch. It restarts the program in memory, allowing me to format another disk. It's a pretty neat feature.

[@nathanaelculver5308]

I’ve been a Z-System guy for decades, where GET POKE and GO has become part of my muscle memory - load a transient into TPA, POKE a value into memory (e.g. to change WordStar’s margin settings on the fly), then GO. I’d forgotten vanilla CP/M doesn’t provide these features.

[@TechTinkering]

I've read a fair bit about Z-Systems and it does seem to have a lot of extra features and flexibility. However, I've never tried it. Mainly because I prefer to standardize around CP/M and prefer the 8085 to the Z-80 - despite recognizing the advantages of the Z-80. Your comment has peaked my interested though, maybe one day I'll give it a go.

[@nathanaelculver5308]

@@TechTinkering As for “standardizing”, Z-System is a drop in replacement for CP/M 2.x/3.x on Z80 architectures (hence the Z-); no 8085 support. The improvements in use and flexibility over vanilla CP/M are legion; had it not appeared so late in the 8-bit computing era, I think it would have had a bright future. Judging by your photo, you’re pretty young to be neck deep in all this retro-tech; ‘Sup with that? :-)

[@TechTinkering]

​@@nathanaelculver5308 Mid-40s, so young according to people in church but, depending on their mood, old according to my children! I first used CP/M on my Commodore 128 at home and also on the Amstrad PCWs at school. I love the simplicity of CP/M. It's great to be able to contain most of the details of a system within my head and I find programming on these simpler systems much more fun. That striving for simplicity is largely why I have centred my interest around the 8085 rather than the Z-80. The opcodes and assembler is much simpler - although I understand that can push the complexity out to the routines which can be quicker and shorter on the Z-80. However, like any decision around vintage computers the choice is fairly arbitrary and governed more my what I enjoy than what is technically better.

[@CircuitBreaker256]

I may have to pick your brains on C/PM! I'm implementing cp/m at the bdos level in my z80 playground system and having trouble with file sizes.

[@TechTinkering]

That does sound interesting. A new BIOS is fairly easy to do but a new BDOS is definitely more complicated. Having said that the interface is pretty well documented. Your best bet for questions to do with implementing a BDOS would be the comp.os.cpm newsgroup. Good luck.

[@CircuitBreaker256]

@@TechTinkering That group looks a bit overwhelming, but I'll give it a go! Thanks for your videos. I have gleaned a lot from them. Here is the hardware I'm working with: kzbin.info/www/bejne/g5LSnYeioJyLga8

[@TechTinkering]

@@CircuitBreaker256 The board looks great. I've just been enjoying some of your other videos as well.