> Do any of the common serial communication handshaking schemes involve just
> the transmit and receive lines?

Very few, if any. Most also uses a ground line.
So, three lines minimum for bi-directional communication.

Besides of that, there are many widely used solutions

- Xon / Xoff
- ACK / NAK
- higher level handshaking
- Application specific "Command" / "Reply" schemes

Jan-Erik.

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