PCB Design |
The prototype PCB was photo-etched in two stages on Wednesday 20th January 2010, and populated/tested the day after.
Since I don't have plated-through hole capability, I've soldered wire between the two layers.
This prototype worked first time (which surprised me a bit, since it's the first time I've used a Xilinx in my own hardware before, and it's only the second 2-layer board I've made at home).
After making it, there are some changes I want to make to the board:
- The reset generator is pretty much redundant - the reset pulse only comes on when the board powers up, and lasts 350ms. The amount of time it takes for the FPGA to power up is longer than that.
- The FLASH ROM configuration device was bigger than I'd anticipated (that'll teach me not to order the wrong part!), and it's a wide SO-8, rather than the narrow version. Luckily, if I'm removing the reset generator, there'll be space for it. For the prototype, I just bent the pins under itself. Unfortunately, I did order 25 of these chips, so I'll stick with them for a bit (I should've ordered the AT45DB021D-SSH-B instead of AT45DB021D-SH-B).
- I didn't realise I hadn't ordered a 50MHz oscillator until midway through construction, so I used a 20MHz one instead. Since the FPGA has clock multipliers/dividers (DCMs), it can cope (unless it's an odd multiplier/divider value).
- The PROGB pin probably won't be required for everything, so I won't solder another one on there unless necessary.
PCB Design |