wrote in message ...

It could go either way... it's just a matter of convention.
*Usually*, a logic value of '1' means high voltage, and a '0' means
ground.

I'm specifically talking about encoders, NOT open collector outputs in
general. All the ones I am familiar with ground on the logic 1.

Yes, the encoder is
open-collector outputs, but the reason for diodes is to isolate multiple
devices connected to it.

The diodes may or may not be required depending on what the devices
interface looks like. Believe me, I've had tons of crap in repeaters tied
to a single open collector transitor for the COS and there were no diodes
present.