Wednesday, August 23, 2017

Cable and board completed for Diablo emulator disk tool for Alto


I have to finish the cable that will hook between the Xerox Alto and my emulator, verify all the wiring and function on the emulator daughter card, then I will be ready to haul this over and use it with our Alto.

Cable that attaches to Alto disk controller card
Other cable end, after ground plane peeled off, before connector attached
The IDC header connector, two rows of 20 pins, will clamp onto the cable end and plugs into my daughter card. That card converts the +5V input signals from the Alto controller to the 3.3V levels used with the Digilent Nexys2 FPGA board. It also takes 3.3V outputs from the FPGA board and drives relatively high current at TTL levels to the controller card. Finally, it implements the end of cable termination with resistor pairs that match the Diablo drive terminator plugs.

Daughter card to do level translations and terminate the cable
I verified that the pins on my board match the cable signal lines 1 - 40 and the connector at the far end. This means that once I have the IDC connector installed and my board is electrically traced for its validation, I should be ready to cable up to an Alto.

By dinnertime, the connector was installed on the cable and checked out. All that remained was to trace each signal line between the IDC connector and support chips, then each line between the FPGA input connector and the chips.

Cable attached to emulator daughter card
The IDC to chip links were all proven good by 8PM, when I turned to checking the FPGA connector to chip lines. By bedtime I completed that task too. I believe this is ready to test on a real Alto, probably this Friday.

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