Basically, the bootstrap is executed from the PROM and is supposed to load the first sector of the disk. ![]() The controller has a small 82S123 PROM for an initial bootstrap loader that starts at $0000 on a machine reset. The controller uses six I/O ports starting (normally) at F8, but my controller wouldn't respond. I also discovered that my drive controller was set up a bit differently than the default Tarbell settings. I needed to change the ports and RDA/TBE values to correspond to my hardware. The BIOS assumed a console output using the MITS 88-2SIO at ports 10h/11h. I started by editing the system tracks of the disk images, then writing the images to physical media using my disk imaging workstation. ![]() ![]() These required minor changes initially and provided a reasonable base for generating subsequent CP/M disks. A number of websites have archived CP/M distributions with the single density Tarbell controller custom BIOS (CBIOS.ASM) and boot (CBOOT.ASM) files.
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