synthings

SYNTHINGS is a digital synthesizer development platform that I've been building.

Revision B boards

jason | 27 November, 2010 19:27

In addition to moving the display connector to the underside of the board, I also took the opportunity to add 4 extra connections for FPGA inputs. While planning how the addressing scheme would work, I decided I didn't have enough address lines.

Adding the 4 lines gave me 18 I/O lines from the CPU to the FPGA. However, I also needed to redo the bottom board to take advantage of the extra pins.

Furthermore, I decided to move the SD card interface to the bottom of the board so I could reprogram the FPGA while the SD card socket was present: it fouled with the JTAG connector with the plug in place.

And I also reorganised the connectors so that they wouldn't foul with the daughter board I made for the rotary encoder (I'd done the daughter board on a prelude to SYNTHINGS - XilSynth).

RevB boards RevB boards RevB boards

With the display in the right place, it looks much more like a real board! The white and black switches have no significance whatsoever - it was merely which two colours came out first from the tray.

I also changed the pattern generator so it did a red/green sweep across the screen - and the rotary encoder changed the blue.

This allowed me to verify something that I'd partially noticed in the earlier test pattern - which was that it appeared as though one of the colour lines wasn't working properly. After a bit of investigation, I found that G[3] was not being set to a voltage. I then tried a few different IO line configurations to see if I could get it to work, but it didn't want to. I finally discovered that there was a hairline break in the track for that signal. A quick run of solder over it (and verifying that no others were affected) got it working.

RevB test pattern

Unfortunately, I didn't take a picture with the blue...

 
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