Stop bits? one lump or two

[Joachim Verghese]

Batz G. wrote:

> Changed to a PC900 which, as far as MIDI optos go, I know work.

Is the external pull-up resistance low enough for fast rising edges?
Most designs have a pull-up of a few hundreds ohms.

Is the optocoupler electrically far away from the UART?
The current through the phototransistor is large enough to
cause substantial voltage drops in longish supply lines.
It might be a good idea to connect the emitter of the
phototransistor directly to the GND pin of the UART.

best,

-joachim