Joshua Shriver wrote:
> Thanks for the info, this is just a personal hobby project and wanted
> to keep it as low as possible. I like the FPGA idea. You mentioned
> getting FPGA chips for $10, do you recommend a place to get them? Can
> you program a FPGA chip kinda like you can a PIC chip? Then put the
> FPGA chip on a breadboard?

FPGAs are usually RAM-based, so you need to program them every time they
are turned on. This can be done by an external microcontroller (such as
a PIC!) coupled with some flash memory, by using JTAG (this is good for
prototyping and debugging, as you avoid the slow flashing process and
just load the design into RAM), or by using an external flash. The
available options depend on the FPGA. Some newer models have the
configuration Flash built in.

FPGAs tend to come in BGA format for most recent devices. You can also
find them in more prototyping-friendly surface mount formats like TQFP
and the like, but you won't find them in breadboardable DIP format. Bear
in mind that FPGAs tend to be more like CPUs to drive and usually
require two or three regulated supply voltages. It is by no means
impossible or even hard to design a circuit yourself using a bare FPGA,
but your best bet for prototyping is to get a prototyping board.

I recommend the Spartan-3E Starter Kit by Digilent. For $150 you get a
500k gate Spartan-3E, PlatformFlash to hold the design, 16MB of NOR
flash for program ROM/whatever you want, 64MB of DDR RAM, an Ethernet
transceiver, two serial ports, a PS/2 keyboard/mouse port, a built-in
USB JTAG programmer, an assortment of LEDs, buttons, switches, and
knobs, a HD44780-based alphanumeric LCD, ADCs and DACs, SPI flash,
one-wire flash, a 3-bit VGA port, a CPLD to control the FPGA bootup and
other things (if you want), an expansion port, and all sorts of other
goodies I'm probably forgetting about. The clock is 50Mhz (or you can
plug in your own canned oscillator instead of the built-in one), but the
FPGA has PLL modules to turn the clock into whatever you want. It also
has several 18x18 multipliers and really fast dual-ported RAM built in.
The development tools are free. You may want to get the matching
breadboard with it ($30-40ish I believe?) which breaks out the Hirose
expansion port to .1" headers next to a breadboard.

The Spartan-3E FPGA is more than large enough to hold a decent CPU, and
has no trouble doing things such as an entire re-creation of the PacMan
arcade system, including the ROM (all in the FPGA, not using the
external Flash):
http://youtube.com/watch?v=MNmp4prf-WQ

You should be able to put a more modern RISC CPU in, though a
full-fledged system with MMU and the likes is pushing it. It should be
doable (you might even be able to run Linux on the thing), but it
wouldn't leave much space for anything else and I'm not too sure about
what clock speeds you can expect from it. Check out opencores.org for
all sorts of pluggable modules you can use.

If you want something like an FPGA but simpler and more PIC-like, I
suggest a CPLD. They are the little brothers of the FPGA and are
programmed much like you would program a PIC (except using a JTAG
programmer, which can be as simple as a couple resistors connected to a
parallel port), and they contain their own Flash. You program them in
Verilog and VHDL as well, but they are more limited in the amount of
logic you can throw in. Don't expect to put a CPU in there, but a bunch
of state machines and logic should be perfectly fine. CPLDs come in
smaller sizes and run on 5V or (more commonly nowadays) 3.3V, single
supply. Packaging is usually TQFP or similar, but I believe there are a
few DIP models out there, if you can find them.

-- 
Hector Martin (hector@marcansoft.com)
Public Key: http://www.marcansoft.com/marcan.asc

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