The RS-232 standard specifies a 12V electrical signal and enough current to drive 50 feet of wire, while the RS-485 standard specifies a 5V electrical signal and current to drive about 1,000 feet of wire.ĭriver integrated circuits vary in quality and performance. RS-232 and RS-485 drivers convert bits emitted by a processor to signal levels that can drive a signal over some distance. That’s where RS-232 and RS-485 drivers come in. It does not have the voltage or current to drive a signal over even a few inches of wire. The processor is designed to interface with other integrated circuits (ICs) so it only emits just enough current to drive an input port in some other IC. Those bits are emitted by a processor out of some pin at processor voltage levels. A microprocessor has bits to send out: a Modbus read holding register command for example. They have nothing to do with what bits are on the wire. The key to understanding RS-232 (and RS-485) is that they are electrical standards. Could it work? Actually, it is possible, but let’s look into it a little deeper. But this week I had a guy who was trying to multi-drop Modbus using RS-232. Sort of like Lawrence Welk and Fifty Cent. RS-232 and Modbus are two words that just don’t go together.
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