4 Nov
2005
4 Nov
'05
9:21 p.m.
On Fri, 4 Nov 2005, Scott Stevens wrote:
On Fri, 4 Nov 2005 20:31:25 -0800 (PST)
"Peter C. Wallace" <pcw at mesanet.com> wrote:
Interesting, and you also get the power planes and bypassing done for you.
Another thing I have have seen is people getting large de-balled BGA FPGAs
cheap from EBay and soldering bypasses and wires to the pads where the balls
used to be (upside down BGA breadboard)
Peter Wallace
Mesa Electronics
On Sat, 5 Nov 2005, Tony Duell wrote:
I think that most if not all of the ISP (In System Programmable) CPLDs have
documented download protocols so that they can be reprogrammed by
microcontrollers. Xilinx even has a smaller binary varient of SVF files (XSVF)
just for this purpose.
Only problem is most of the newer, easy to program parts are in surface mount
packages, though PLCC 44s are not too bad. A Xilinx 9536XL in that package is
about a dollar, a 9572XL about $2. I Believe someone has made a complete CPU
(but no memory) in a chip somewhat smaller than the 9536...
An interesting development that I have noted is people selling modern FPGA
chips on salvaged boards on eBay, i.e. the chip all soldered onto a card and
ready for hobbyists to fool with. I am talking about 'salvage' boards,
meaning in at least several instances it looked like the area of the board
with the FPGA on it had been cut out with a tinsnips. The FPGA and board
was salvaged from some bigger project.
In many designs, there is a hole-per-pad zone surrounding the whole FPGA for
testing purposes, and the chips can be 'recycled' in this fashion pretty
easily. It gives people who want to fool with these chips an easy way to
get at them without needing to do any fine-pitch SMD soldering. Sort of the
poor-mans 'development board' (i.e. the more pricey eval boards that Xilinx
and Altera sell) Unfortunately, many of the more interesting TTLs
are now no longer
easily available (you find lots of octal
drivers and registers, but almost none of ALUs, multifunction chips,
RAMs - even the classical
7490,7491,7492,7493 combo of counters for any purpose is reduced to
7490/7493 - noone
needs to divide by 6 ('92) any more - you don't build digital clocks in
TTL) - you have to seek for
them in specialized mail-order shops. This is no issue for us old farts
who play with such stuff for
long time, but it is another hurdle for starters. A kit with all parts
is much easier to acquire - but then,
Waht somebody needs to do (and it can't be me for obvious reasons) is to
select some CPLDs/FPGAs where the download protocol is documented (that
is, you can progam the chip, given the binary file, without a proprietary
programmer), and use the tools (that's why it can't be me) to make some
useful logic functions -- things like an <n> bit universal shift
register, <n> bit ALU, counters, even JK flip-flops, gates, etc. Make the
binary files available for free download.>
Anyone wanting to experiment with logic and not wanting to use the
horrible CAD tools under an even worse OS, can then program up some chips
with the appropriate files and use the resulting devices like the TTL of old.
-tony