25 Nov
2009
25 Nov
'09
6:20 p.m.
Joachim Thiemann wrote:
I'm currently teaching myself VHDL using the free
Xilinx tools ("ISE
Webpac" or something), using a Spartan3E board
Which one? I've got the Digilent Spartan 3E starter kit. Nice because
it has built-in programmer, ethernet, vga, lcd, etc etc.
I'm in a similar boat and trying to learn Verilog.
I'm planning to use the Xilinx chips with my old
Commodore stuff too,
and one of the problems is the use of 3.3V rather than 5V logic.
Right. This is one place where the straight Spartan-3 is nice because
it was 5v. The Spartan-3 aren't as big, so they aren't as flexible etc.
official recommendation from Xilinx for their Spartan
devices is to
use simple resistor for connecting 5V out to 3.3V in, and just connect
straight-through for 3.3V out to 5V in.
Yes, the value that comes to mind for doing this was 220 ohms. Xilinx
makes boards that are designed to connect to 5v logic, in that case,
they simply put resistors in line on the board itself.
I have no idea how I'd handle
a bidirectional port though; is a resistor good enough or is a level
shifter needed?
That's my (limited) understanding -- that you need a level shifter.
I was nearby McGill University in Montreal a few years back. Stayed at
the Ritz Carlton on Sherbrooke West. Grabbed breakfast at Tim Horton's
now and again.
Greetings from another FPGA newbie.
Keith