Philip Balister wrote:
First, let me get this off my chest, I take a "few" years off from
hardware design and all of a sudden there are more logic voltage levels
than I have fingers ....
So after a conversation in #gnuradio we have figured out the $200
Cyclone III dev board only supports 2.5 volt IO. I need to interface
with the Beagle Board expansion connector at 1.8 volts. Basically, we
need to configure one bank of IO for 1.8 volt IO to talk to the Beagle
Board Expansion connector. This does not look practical with the low
cost Altera board (and looking at the higher end boards, nothing jumped
out at me as solving the problem)
Rather than wait on a Chris to make a board so I can start working on
the interface, does anyone have any good idea on connecting an FPGA to
the Beagle Board expansion connector? At this point I don't care who
makes the FPGA :)
Digilent does mostly Xilinx-based FPGA development boards. Their Spartan
3E Starter Kit provides a 500k gate device with plenty of I/O (Ethernet,
LED, switches, buttons, rotary encoder, LCD, VGA, DAC, ADC, expansion
connectors, etc).
http://www.digilentinc.com/Products/Detail.cfm?Prod=S3EBOARD&Nav1=Products&Nav2=Programmable
There is a 40-pin Hirose connector on the right side of the board that
mates with some standardized expansion boards and provides 43 I/O pins.
The voltage levels on these I/O signals are jumper selectable to either
3.3V or 2.5V, but if you were to provide an external 1.8V you could use
that (would require a separate wire to the center pin of J9 on the board).
This board is $150 and a mating expansion board with uncommitted 0.1"
thru-hole grid is another $20. The on-board FPGA is programmable with
Xilinx's free tools, and the board provides a USB<->JTAG interface for
configuring the FPGA and flash.
Not an ideal solution long-term, but definitely an excellent way to get
a head-start on SDR interfacing. Mid-sized Spartan 3E parts are
available in non-BGA/CSP packages at reasonable cost for small
quantities (<$30) and would be fairly easy to design-in to DIY projects
with inexpensive PCB fab processes.
Eric
