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Re: [Xylo-SDR] Cyclone II board
It's always worth a little extra PCB real estate to make the board as
general purpose as
possible within reason. Several headers with unused pins are desirable,
every unused pin to a small pad or via which will accept 30 ga wire has
been my lifsaver
more than once. It's good to use a FPGA layout where a larger part could
if desirable, in the case, the EP2C8, which would provide twice the
number of logic elements.
The EP2C8 has a few less I/O pins and a few more power pins. If the pins
tying all the EP2C8 power pins to Vcc or gnd, and using only the I/O pins
available to the EP2C8,
then either part can be used on the board. Never can tell on a project of
this sort what else
someone might desire to also stuff into the FPGA someday.
(I'm always disappointed that there are seldom more than two sizes of
CPLD's or FPGA's
available in the same footprint and never more than 3)
At 09:09 AM 12/11/2005, you wrote:
As I mentioned on
the Softrock forum, I'm working on a small system like the Xylo, but
using the newer, bigger and better Cyclone II EP2C5T144 FPGA. The
forthcoming KNJN Saxo board probably uses it. My board will just have the
parts for an SDR on it, PIC18F2455 for FPGA configuration download and PC
comms, the FPGA and a suitable ADC (probably the Wolfson one), and will
be very cheap.
I've been told that the '2455 doesn't work properly for
full-speed USB 2.0, but can't seem to pin this down. I've just designed a
small home-made PCB with just the '2455 on it that I can try out, before
I commit to using it with the FPGA.
I've got some EP2C5T144 chips on order from Altera (about
$12 each plus shipping etc.), and should get them next week. I've created
the EP2C5 part for the Pulsonix PCB software I use, but need to finish
off defining the pin net names, which will minimise the chance of design
errors. Altera has a useful spreadsheet for the pinouts, which saved me a
lot of time as I could just copy/paste the pin logic names into the
Pulsonix part editor.
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