Re: FPGA

On Mon, 6 Oct 1997 16:03:27 -0800, you wrote:

>>G'day Clay (and folks),
>>
>>A while back I looked at putting the whole Cinematronics board onto a
>>single FPGA. However two obstacles that I ran into were the RAM and the
>>I/O pins. In your letter down below, Clay, you said that SRAM chewed up
>>alot of the FPGA. Does that hold for dynamic RAM like the 256 words by
>>12 bytes of RAM on the Cinematronics board?
>
>(I'm no FPGA guru, so I'll give you the 50,000 feet explanation as I
>understand it.)
>
>In an SRAM, each group of gates/cells can effectively store a bit of
>information (the chip die is layed out to access the bits in what's
>effectively a big matrix). This gives pretty good memory density since
>it's specifically designed for this memory matrix.

My understading is that is takes four transistors per bit setup as a
Set/Reset latch.

>DRAM's use a simpler (smaller) group of gates/cells to store each bit, this
>gives better bits/sq inch, but requires a periodic "refresh" to keep the
>bit values.

In DRAM they use 1 transistor and a capacitor. Unfortunately the capacitor
will discharge quickly, so it must be *refreshed*.

So I believe this makes DRAM nearly four times the storage density of SRAM
for the same die size.

<snip>

>>ps - These PIC intrigue me....how do they compare to FPGA for quick/easy
>>implementation?
>
>The PIC's just a microcontroller for all intents and purposes. (Actually
>it seems a LOT like a PDP-8 ;-) They're cheap (like $2.50 for a 16C54),
>pretty quick (20MHz clock = 5 MIPS), and have a very nice (free)
>development environment called MP-LAB that has an assembler and simulator
>and whatnot.

It IS a lot like the PDP-8 (I've described it that way myself). I still
have a programmer's reference manual for a PDP-8. Some company started
making a PDP-8 on a single chip for a while there, I wonder if it's still
available.

The PDP-8 clone I used to program back in a Jr College was a completely
wire wrapped work of art. All TTL and a *lot* of wire wrap.

I'd sure like to have that now, it would make a great room heater. I
wonder if you could write software loops that would cause it to give off
different amounts of heat and use it as a self regulating heater...

-Zonn
Received on Mon Oct 6 16:29:49 1997