Hey guys, I'm fairly certain this is a serial board - mostly because the PO told me so, and when I received it, it had a 25-pin male connector on a three-wire cable carelessly soldered to the pads behind one of the cable headers on the top edge. But the cable was removed as a matter of course when I was prepping the machine for a rebuild. I mistakenly assumed that the docs would be trivial to locate - so no need to record the original wiring connections.
. On Thu, Oct 1, 2015 at 12:26 AM, tony duell <[email protected]> wrote: > > > I couldn't spot how they did level shifting to RS232 levels. The SI > > signal appears to go to a 7400 next to one of the Uarts. > > There are a couple of 8 pin ICs near the 10 pin headers, they look to > be 1458 dual op-amps (I can't exactly make out the numbers...). > > Op-amps were often used as RS232 drivers. Give them +/-12V supplies, > feed a TTL signal into one of the inputs, connect the other input to a > voltage between the TTL levels (potential divider from the 5V line) and > apply no negative feedback. The Op-amp output will swing between the > supply rails. > > -tony >
