Olympia Olytext 20 OS question.

"Ernest" <ernestls(a)home.com> wrote: > Hi Don. I may be able to get a copy of CP/M-80 but it won't be for my > specific system. That's the problem. I don't have the OS for it. That's why > I was curious about how difficult it would be to set up a generic copy of > CP/M to run on it. I've never assembled (?) CP/M for a computer, but I've > been reading a how to on doing it, and interested in giving it a shot. I'm > not even sure of how to load/run the system monitor to ID the various > address' but the thing is, as with anything, there's always a first time, > and you have to start somewhere. >

Hi Ernest Most of CP/M is generic but the part called BDOS has to be specifically written to work on your computer. This part contains both the disk, printer, punch and serial I/O. The most important are the disk and serial. Usually the serial is easy because there were only a limited number of serial chips used. You don't have to make the serial interrupt driven. It is easier to make it a simple polled system at first. I've left mine as a polled system because I see no need to setup serial when I'm the only user. The disk I/O is a little more difficult. You'll need to know how the disk interface works. Most of the newer disk interfaces use one of the Western Digital series of chips. The reading and writing of sectors is relatively easy. You'll still need to have some understanding of disk formats and how the sectors are addressed. If you can find examples of code for the interfaces you have, 95% of the battle is won. You'll need a way of getting the code into the memory and then to the disk of your machine or someone else with a running machine can create the disk. The IMSAIs have the advantage that they have front panel switches. The machine may have a ROM based monitor that can be handy. If not, you'll need another machine to help boot strap your machine. The other machine doesn't need to be the same type, it only needs to be able to write the same disk format. I brought an old IMSAI back to life by doing a BDOS for it. It had an AY-3-1015 serial chip that was typical of the older machines. These are generally easy to work with since there is no software initialization ( other than clearing power up trash ) that needs to be done. The 8251 and 8250 type parts require initialization but they are also more versatile. The disk interface, on my machine, was an early TTL interface that had DMA to the machines memory. This took me quite a while to figure out and it wasn't until I found a schematic that I was able to figure it out ( it also was broken ). Luckily for you, most of the newer interfaces use standard chips and are easier to deal with. In many cases, you can make progress without schematics and only the chip manufactures spec sheet. It is also possible that many of the functions you need are already in ROMs on your machine. Dwight