Friday, December 2, 2016

Prepping for next Alto restoration session, debugging emulator function of disk tool


I made progress on the emulator role, which is now reliably modeling the rotation of the disk, emitting SectorMark signals and the proper SectorNumber values. However, I am getting nothing from the ReadData and ReadClock lines yet.

I saw a few polarity errors, where I was blocking the outgoing signals on the wrong condition of such states as SelUnit1 and FileReady, which I corrected. I still didn't see the read data emitted, which I traced down to a test bed flaw that was commanding continual seeks. This forces the ReadyToSeekReadWrite line off, blocking the read process.


I picked up a few items we need for our next stage of work on the Xerox Alto II we restored. One of the mice we have is the optical type, the Lyons mouse, but the cable on it did not match the connector on the Alto. As well, we are early in working on an Ethernet bridge but don't have ethernet working as yet.

Al Kossow had a broken Hawley (mechanical) mouse and donated the PCB with its cable to us. On the Hawley mouse, the cable is directly soldered onto the PCB but uses a ten pin Amp connector to hook the cable to the Lyons mouse.

I desoldered the cable from the PCB, soldered on pins and inserted then into the AMP housing. Hopefully it will work properly when we hook it onto the Lyons mouse tomorrow.

Al also loaned as an Ethernet transceiver, which  we did not have, so that it is easier to debug than our attempting to drive the controller card with a BeagleBone developed by Ken. Once we know the board is working and that we can study all the signal timings to make the BeagleBone unit work right.

Tim will bring over another transceiver too, just to be sure we have one that works properly. Both of them are set up to connect to a 75 ohm coaxial cable, the actual ethernet line used with the early 3 Mb LAN. We need a 75 ohm cable of at least a half wavelength and a terminator. Hopefully we will have a cable on hand. 

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