nessus@nsc.UUCP (Kchula-Rrit) (02/16/84)
> I am considering building a homebrew computer system and would like > to make it CP/M compatible. Anyone have any ideas about designing such > a thing{hardware and software}? The system will be using Multibus(tm) > boards and card cage. > > Please do not advise me to go and buy XYZ system. My budget cannot > afford buying a computer and I collected the necessary components{disks, > RAM, and such} from my company electronics club. > > Kchula-Rrit > !menlo70!nsc!nessus I neglected to mention that I have some Multibus(tm) boards. 8080 CPU, 64K RAM, and disk drives. For budgetary reasons, I may have to design a floppy-disk controller. Any advice/horror stories/gotchas? Kchula-Rrit !menlo70!nsc!nessus
bcdoody@wateng.UUCP (Brian C. Doody) (02/29/84)
Since a reply to the Author's mail wouldn't go through, I'm posting this response to the net: Regarding your request about information designing a FDC board: I've also built a homebrew system (8085a-2 CPU, 64K, 1 5.25" dsdd disk) and since it is entirely non-standard (i.e. my own bus, etc) I had to do everything from the ground up, including the FDC. I've heard that the Western Digital 279x series of floppy controllers are the easiest to use, although not as flexible as some others. I found, however, that they were too expensive for me (At least in Ontario, Can.) so I went with the Intel 8272/NEC upd765 (they're both the same). I have two references which together provide enough information about how to build the controller around this chip. They are: NEC Application Note 8, "A Single/Double Density Floppy DIsk Controller Using the upd765", by Richard Weiner and Gregory York. "Build the Circuit Cellar MPX-16 Computer System, Part 3", by Steve Ciarcia, Jan. 1983 Byte. I think Ciarcia's design is based on the NEC app note, but it provides a more thorough controller (i.e. all the options you'd ever want). I've built the controller but am still waiting for the 8272 via mail order, so it hasn't been tested. If you want to get CP/M up and running you'll need some info on how the disk is set up and how to write a bootstrap and all that. A wonderful book on that subject is "The Programmer's CP/M Handbook", by Andy Johnson-Laird, Osborne/ McGraw-Hill, 1983. It was $30 (Can) and worth every cent - it's far and away the best book I've seen (and I've looked at a lot of them) and leads you through step by step, telling you everything you need to know. It includes a simple BIOS (which you'll need to write) as well as a more advanced one you might implement once the beast is running. He presents all the source code (8080 asm, tiny bit of C for some utilities) and offers a disk of it for $50(US). IF you're not using the standard 8" sssd cp/m format, it's wise to make it the same as some available 5.25" system on the market today, so you can buy software on disk. I'm trying to make mine Superbrain QD compatible (because I know someone who will give some useful things he's written on his Superbrain) but that's a bad choice because the data is stored in inverted form, so you need special "invert-before-store" disk routines. It seems manufacters are not too willing to tell you their format, either. Format incompatibilities lead me to suggest the standard 8" sssd CP/M format if you can afford the (usually) extra bucks for the bigger drive. Good luck! Brian Doody University of Waterloo Dept. Elec. Eng. Waterloo, Ont. Canada