The serial interface RS 232 is a full-duplex point-to-point connection. Full-duplex means that data can be both transmitted and received simultaneously via the interface and that only two devices can be connected with each other. If two devices are to be connected to a computer, then a second interface port is required on the computer. The two connections are totally independent from each other. This method has a disadvantage, because interface cards for PLCs are expensive and with PCs a maximum of 4 ports are available for use. For this reason, more recent Kübler counters are equipped with either the RS 422 or the RS 485 interface. At least a 3-wire cable is needed when connecting RS 232. The connection then works without handshaking. For connections with handshaking a 5-wire cable is needed.
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