On Sun, 21 Oct 2007 23:36:12 -0400, "Tom Del Rosso"
wrote:

"John Larkin" wrote in
message news
This its the first article of a new waveform generator. It took me a
while, an hour or two, to find a stuck bit on the uP data bus; turned
out it was a bad solder joint on one of those tiny quad resistor
packages. Something about their geometry makes them hard to solder and
hard to inspect.

Seems as though the most reliable thing we solder is BGAs. Who woulda
thunk it?

That may be the first DIP socket I've seen on one of your boards.

That's for the eprom. It holds the uP code and the fpga configuration.
I like using plugin eproms, because if we change anything, we can send
the customer a new chip and he can just plug it in. If we use flash,
field upgrading is a lot trickier and riskier.

The two extra pins are for debugging. One is the microprocessor \WRITE
line, and one is +3.3 volts. When we test code, we plug in a little
ram board instead of the eprom, and load it through the bdm port, the
little 10-pin header.

Of course, they are otp eproms, sort of an oxymoron, but that's what
most people call them.

John