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13 Serial
communication
13.1 General
Description
Every ETC contains at least one serial interface RS 232 which provides different functions. The
following table shall give an overview:
COM1 RS 232 Front
COM1 RS 232 Back
COM2 RS 422
ETC 12(R)
ETC 14(R)
ETC 24(R)
The interface COM1 can either be connected via the RJ10 front panel connector or via terminals
while COM2 only can be connected via terminals.
If a cable is connected to the front connector of COM1 (RJ10), the terminals using the same
interface are disconnected.
Notice:
RS 485 - Operation:
The interface COM2 can also be used as a RS 485 interface. In this case
the terminal pairs TXD+ / RXD+ and TXD- / RXD- has to be connected
together. When no data is transmitted, the interface driver always becomes
tristate, even in RS 422 mode.
Requirements for the cabling (RS 422, RS 485):
- Twisted Pair cable
- Signal GND – wire necessary
- Terminating resistor of 120
(at the end of the bus cable)
- Max. 32 devices on one bus
- When using cables longer than 30m, screened cable should be used.
