Tuesday, June 14, 2016

Xerox Alto CRT driver tool completed and sent to team


Another team member had previously measured the video signals on an Alto, which gave me the data I needed. The horizontal line scan takes 38 us, with a 3.56 us sync pulse and appropriate front and back porch times (blanked intervals that bracket the sync pulse), it delivers 606 pixels of video in a line with the 20.16MHz pixel clock.

Vertically, it operates in interlaced scan mode at 60 fields per second, alternating odd and even lines of the display memory buffer on each scan. The 16.67 ms vertical interval has a 152 us vertical sync pulse and with its front and back porch times, permits the 404 even or odd lines to be scanned. To address the interlaced lines, the even field will have the vertical sync pulse delayed by 19 us, half of a horizontal line.

I wrapped up the logic for the tester and built a few patterns. It generates vertical and horizontal bars, vertical and horizontal lines, with various shifts in position. To help the other team members while I am away on my trip, I wrote up a very brief manual for using the tool. Everything was transmitted over to Marc before the end of the day.

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