I've always thought that in serial-type comm (rs-232, rs-485, etc.), many of the devices that do not have RTS or CTS test the wire before they start transmitting on TX. So, to be sure that another device is not already transmitting on the wire, they test to see if the wire is a source, a sink, or Hi-Z. I thought the pull-up or pull-down resistors were to help with this.
Real RS-232c (12v) and RS-423 (6v) are bipolar-unbalanced signals and only allow a single transmitter but multiple receivers. Some systems only send a unipolar signal, which might work, but isn't to-spec. RS-232c.
RS-422 is a bipolar-balanced/differential pair, also single transmitter.
RS-485 is also a bipolar-balanced/differential pair, but you can have multiple transmitters on the line (they're supposed to go to a high-impedance state when not sending).
Of those, only 485 can sense that another node is sending, and AFAIK only if it specifically implements it.
The only serial bus architectures that I can think of which implement collusion-detection as part of the spec are things like Ethernet, Arcnet, and some of the coax/twinax-based PLC and data networks.
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I think we're being unclear about the purposes here- pull-up/down and termination serve different functions and go in different places- terminators go at each end of the line/bus, and the pull-up/down can go anywhere, but usually only once. The pull-up/down network may incorporate termination as the middle resistor, but doesn't have to.
The relationship between pull up/pull down and termination resistors comes about when you have a single ended rather than a balanced differential signal.
With a balanced signal, you can run a termination resistor from one lead of the pair to the other and as long as the driver can handle that load you have done the job of avoiding reflections.
But with a single ended signal you have the problem of where to connect the other end of the terminating resistor.
I'm with you on the balanced line termination, except that for almost any type of signaling, the terminating power dissipation is usually rather small since the drivers limit the current and you shouldn't use more terminators than called for. For an unbalanced line, there is no problem of where you connect the other end of the terminator- you connect to the signal reference.