Sunday, August 21, 2016

Finishing design work and starting construction of Xerox Alto - Diablo disk tool


I began the design work for the tool we will use to test out and drive Diablo disk drives, which also will act as a physical drive to emulate and replace a disk cartridge with a PC based file. I am leveraging my Digilent Nexys2 fpga board as the foundation of the tool.

I had to very carefully spec out what behavior the emulator has to present to look like a real disk as well as what it has to deal with to drive, read and write on the real drives. This involved reading documentation, schematics, Alto microcode and looking at investigations done by Ken Shirriff into the same source materials.

I should be able to start building up VHDL code this week and to solder up the cables and related interface hardware that will be needed. Careful advance planning will save a lot of wasted time later, which is why I am doing all the up front work.  The parts for the level shifting boards are on order.

FX2BB, top (Without Breadboard).
The extension board for the Nexys2 FPGA board that will make wiring easy


  1. I'll be following this project carefully - hopefully, some of this may translate over into an RK05 emulator for the DEC folks. It would be great to run the drive and read/write data from a PC as well as going the other way and using the PC as an emulated drive on the real controller.

  2. Hi Jack

    Yes, it would be pretty easy to evolve this to an RK05 driver/emulator. Very similar technology to the Diablo drives, as are 2310, Pertec and others. It would simply mean different extension boards plugged into the fpga board and some additional code to adjust for each variant:
    drive type
    number of sectors
    . . .