Yet another reason to use an operating system that doesn't enforce such
arcane requirements intended as part of an insidious content protection
systems that prevent one from acquiring ones own data.
Bruce
Bob Camp wrote:
Hi
No Windows 7 driver signing issues with a serial port. USB can be a bit of a
tangle that way, not as easy as it used to be.
Bob
On Feb 17, 2010, at 7:20 PM, Bruce Griffiths wrote:
Lux, Jim (337C) wrote:
I don't know if there's a FIFO in front of the UART (e.g. what if you get
simultaneous zero
crossings).. but I would expect there is.
The "hard work" is in the zero crossing detector ahead of the FPGA. (and
perhaps in the latching of
the ZCD inputs into the FPGA).
Given how long ago it was made, that FPGA isn't a huge one.
Using 8 flag bits (one per channel) together with the associated time
stamp is a little more efficient and very easy to do and it doesn't
require a FIFO to ensure that simultaneous zero crossings aren't missed.
Still need the FIFO..
Say you got one zero crossing at 0x01000 and the next at 0x01001 (where the
number is the 20 bits in hex).. you'd still be sending the characters out the
UART for the 0x01000 crossing when the next crossing occurred 10ns later.
If I were doing it today (and I have no idea how Steve built it 10 years ago),
I'd do something like a character for channel number and direction (ascii 0
through 7 for positive going, 8 through F for negative going) and 5 characters
for the count (in hex), followed by a carriage return. All printable
characters, easy for testing, no hiccups with DOS or some device driver trying
to interpret binary, etc.
You've got 8 channels, each zerocrossing at about 200-300 Hz (the difference
frequency is 123 or 124 Hz, so you get twice that many zero crossings), or
about 1600-2400 messages/second. At 6 characters per message, that's about
10,000 characters per second, so you'd need a fairly fast UART to keep up.
(OTOH, the article mentions dropping characters..)
They might have only used one direction of zero crossing, which gets you down
to the 5000 characters per second, which you might be able to squeeze into a
38.4kbps serial stream, especially if you go to a denser packing. But you'll
still need a FIFO.
Next time I see one of the FTL guys, I'll ask.
Jim
A LAN, USB or Firewire interface may be more appropriate all are easy to
implement.
Bruce
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