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Wiring Fundamentals: RS232 Communications

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RS232 Communications

01.55

00:00 - The RS232 communication protocol, also called the serial communication protocol, has been around since the early 1960s and until CAN communication started to become commonplace, was the standard for data communication in the automotive aftermarket.
00:14 CAN has now largely supplanted RS232 but you do still sometimes strike devices that communicate with the protocol so it's worth knowing about the wiring requirements.
00:24 An important difference to be clear on between RS232 and CAN is that RS232 is only capable of communication between two devices.
00:33 It's not strictly a network like CAN is where you can have many devices all talking to each other at once.
00:39 Devices that use RS232 will have two or three pins dedicated to the task.
00:43 A reception pin, a transmission pin, and possibly a dedicated ground reference pin.
00:49 Using twin core shielded cabling, you connect the transmission pin of device one to the reception pin of device two.
00:56 And then the reception pin of device one to the transmission pin of device two.
01:00 You should always have a transmission pin transmitting into a reception pin and vice versa.
01:06 The rules for grounding the shielded cable braid at one end are the same as when using shielded wiring for a sensor signal.
01:12 In this instance the use of shielded cable is less about protecting the RS232 communication wires from external electrical noise as it is about protecting the rest of the wiring from noise radiated from the RS232 wires.
01:26 The RS232 protocol uses a plus minus 12 volt signalling level which can have enough energy to generate noise in nearby devices.
01:35 If the two devices have a dedicated ground reference pin for the RS232 communications, wire these to one another using standard wire.