Hi again,
I would like to power the whole thing from USB, using something like this (http://www.droids.it/data_sheets/990.004%20datasheet.pdf), assuming it could correctly handle the USB power negotiation (digilent will go way past 100mA).

The output can be either 3.3 or 5V, so I see 3 options:

1) Bypass the onboard serial converter
2) Insert a 3.3--> rs232 converter
3) use J1 connector on the fpga board with a minor modification to VHDL code to use J1 as the serial port

Any ideas?

Giuseppe Marullo

I have a FTDI USB/serial breakout board that is very similar: http://www.zbasic.net/Interface-Kits/USB-TTL-Serial-Converter/p-42.html. It should be possible to connect the 3.3V power and TTL serial lines from this board to the Spartan3 board. Unfortunately they do not provide a schematic for the breakout board that you list so we cannot be exactly sure how it works. The datasheet does seem to suggest (and it looks correct) that if you connect pins 8 and 9 that you will get 3.3V TTL signals on the TX/RX pins.

As you suggest in options 2 or 3, you can either use RS232 converter and plug into the DSUB 9-pin socket or connect to J1 auxiliary header on the Spartan3 board - see pages 33/34 in the Spartan3 reference manual. to use this header also requires a change to the la.ucf file to point to the header (N10, T14) rather than the Maxim serial converter (T13, R13). Look for lines 118 and 129 in the la.ucf file.

This looks very doable but I haven't tried it.

Mike
oakmicros.com

I tried powering the Spartan3 and omla32 from the USB 5V supply and it worked fine for me using the FT232RL breakout card mentioned in the previous append.

Great news, but if you are using the USB 5V I could do the same nuking the US232R-10 and getting the power from it.

Can you confirm exactly where did you connect? I could even get the 5V before the serial adapter, provided that said adapter is always plugged to ensure proper power negotiation.

This has the added value that there is no VHDL change and no added converter between the board and the USB.

A fancy enclosure is the next thing to implement...

Giuseppe

I plugged into the 5V that comes directly from the USB socket. In the schematic below it is pin 3 of the J5 jumper. Note that this jumper is in the 1-2 position to make sure that 3.3V levels are sent to the FPGA for TXD-A and RXD-A.

You might have similar access to 5V on your USB adapter. I cannot tell because they didn't publish the schematic.

Mike
oakmicros.com