Friday, June 27, 2014

Breakout board for Terasic Cyclone V GX Starter kit

Project
I wanted to be able to use the PMODs I bought for my Digilint Nexys2 with my new Terasic Cyclone V GX Starter kit. Also I would like to be able to hook up a keyboard.

Design criteria
The HSMC connector is not particularly hobbyist friendly, I could only find one place that sold them and they are cost prohibitive. The GPIO connector looks good, but shares most of its lines with either the Arduino Shield connector or the 7 segment LED module.

The PS/2 connector uses two of the six unshared data lines. The four PMOD connections use all 14 of the LED display lines plus two of the unshared lines

Assembly notes
Make sure to put the key on the 40 pin connector towards the edge of the board.

1) Solder 40 pin connector to board
2) Solder PMOD connectors to board
3) Solder PS/2 connector to board

Programming
PS/2
Clock - GPIO[0]
DATA - GPIO[1]

PMOD
A1 - GPIO[23..20]
A2 - GPIO[27..24]
B1 - GPIO[31..28]
B2 - GPIO[35..32]

Manifest

Total cost: < $20

Afterthoughts:
  • If I make another version of the board, I should make the board a little wider; the PS/2 port is a little crammed
  • It would be nice to add jumpers to select between 3.3V and 5V for the PMOD and PS/2 connectors
  • There are still 2 unused data lines that could be repurposed for a I²C connector
  • Why do all these starter boards include rather wasteful 7 segment LED display designs. At least the Nexys2 board was multiplexed, only using 12 data lines for the display. The C5G board uses 48 data lines and doesn't even give you access to the DP line. With I²C I could drive 32 digits with two data lines.
  • It was cheaper to design a custom adapter board than to buy proto board and cut down to size.
  • I should get the files into some sort of SCM instead of on google drive

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