PDP-11/23 up and running RT-11

On Mon, May 24, 2004 at 08:33:39PM -0400, David Betz wrote: Hmm... maybe you should check your comm ports... I know that's one thing that's inconsistent in the DEC world - reliance on -12V from the bus. The first rev of Qbus COMBOARD pulled -12V from the bus for the 1488/1489 EIA level shifters. We shipped a board to an early adopter and it failed. Apparently, that particular chassis did _not_ provide -12V (I don't recall what the customer had, but we would have tested our design in a BA-11M and a BA-23). Rev 2 has a +5/-12V converter in the lower corner. I still have a gross of them from unbuilt stock. Many modern designs have moved to MAX232-like drivers; we might have, too, except we were supporting two fully-handshaked sync serial ports - that's a lot of MAX232 chips and (at the time) expensive tantalum caps. I think our cost on the voltage converters was on the order of $12-$17 each, which was marginally less expensive than changing driver chips, but the engineering to retrofit it to an existing design was trivial. We also drove 50' cables routinely... not sure how well a MAX232 works over longer wires. -ethan -- Ethan Dicks, A-130-S Current South Pole Weather at 25-May-2004 01:00 Z South Pole Station PSC 468 Box 400 Temp -82.9 F (-63.9 C) Windchill -112.7 F (-80.40 C) APO AP 96598 Wind 5.9 kts Grid 048 Barometer 672.3 mb (10917 ft) Ethan.Dicks(a)amanda.spole.gov http://penguincentral.com/penguincentral.html