"Colin Constant" wrote:
> Sorry, you lost me with the last sentence.  Why do I need a resistor in
> series withthe incoming line followed by reverse Schottky diodes to power
> and ground?

Basically, Olin is suggesting that you take two Schottky diodes (D1 and D2),
and:

    - Connect anode of D1 to the signal line, and cathode to Vcc
    - Connect cathode of D2 to the signal line, and anode to Gnd

What this will do, is protect the Rx input by keeping the voltage on the
signal line from going above Vcc, and below Gnd.

-----

However, there's another way to do what you're trying to do. In automotive
networks, there is a concept of "recessive" and "dominant" states. What that
means is, if you put both on the signal line, the dominant state wins.

The way to accomplish it, is with an open collector driver. If you use an
NPN transistor, put a weak pullup (say, 1k) on the signal line. In this
case, +5V is the recessive state, and 0V is the dominant state.

If you use a PNP, use a weak pulldown.

You may be able to do the same thing with OC pins. You would have to use
larger values for the pullup/pulldown, which would limit the communication
speed.

Best regards,

Vitaliy

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