An unpowered board will actually draw some current from the GPIB bus, via the Atmel chip's protection diodes I'd imagine. Enough to light the LEDs dimly. To avoid latchup concerns, it's probably a good idea to connect the USB cable before the GPIB.
I don't see this happening on the newest board (version 4.20 firmware, with the nice metal housing). I've never actually seen it cause a problem, but when troubleshooting, it's one possible thing to eliminate. You can try sending the command ++rst to force the Atmel chip to cold-boot itself. That takes about 5 seconds. -- john, KE5FX > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Behalf Of John Ackermann N8UR > Sent: Sunday, April 15, 2007 1:19 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Prologix GPIB/USB converter help... > > > Just an update -- I have things working more-or-less OK now, after > messing around with line terminations and timing. > > However, there *is* a problem, at least on one of my systems. If you > plug the adapter into the USB port with an active device on the GPIB > side, things go nuts and that yields (at least with the Austron 2100F > receiver I had on the bus) the > every-character-typed-echoes-a-question-mark problem. If I connect the > USB first, then the GPIB, that problem does not occur. > > I haven't yet figured out if a device clear or interface clear command > will correct that. > > John > _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
