On Tue, Apr 12, 2022 at 3:46 PM Fred Cisin via cctech <cct...@classiccmp.org> wrote:
> >> There's a 2K hole in the Model I memory map above the ROM > On Tue, 12 Apr 2022, Yeechang Lee via cctech wrote: > > Is this the hole that causes stock Model I to not run CP/M? > > NO. > The problem with CP/M on TRS80 is that CP/M expects RAM from location 0 on > up. When I was a freshman at Purdue, I lugged my Model III to my dorm room and connected to the ECN network with a 300 baud modem. I used a local editor and wrote a Pascal program to upload my Pascal source to the dual processor VAX-11/780 (Google George Goble), ea or eb, (I don't remember) that was used by our introductory programming class. The terminal program I had was something I found in Byte magazine in assembler and I modified it for the TRS-80. I had BASIC, Assembler and Fortran on the TRS-80 M III, so it was probably all in assembly. There was an article in Byte about CP/M for the TRS-80 Model III that described a hack to swap the ROM for RAM. The idea was to invert bits A15 and A14. That would move the ROM and keyboard from 0000 to C000. There was a spare bit in some 4 bit register, so all you had to do was cut a couple traces and insert some XOR gates. I remember doing the modification on a Saturday while listening to the Purdue football game on the radio. I put it all back together and it worked. WoHo! At that point though I had no access to CP/M or where I might get it legal or otherwise, but I was good to go when I found it. I still have the computer and I still have the Byte copy. So 37 years later I should try to complete the project. -chuck
