1 Slave at the bus line end, bus termination with 120 Ω resistors
2 Master within the bus line, pull-up and pull-down activated
3 Slave within the bus line
4 Slave at the bus line end, bus termination with 120 Ω resistors
The following photo shows a wiring example "master within the bus line", wired at the COM1
bus connector of the terminal base:
If the bus is operated with several masters, the pull-up and pull-down resistors
may only be activated at one master.
The earthing of the cable shields of the bus lines are described in the CS31 system bus
(PM57x, PM58x and PM59x)
Ä
Chapter 2.6.4.8 “CS31 System Bus” on page 1282.
2.6.4.7 Serial Interface COM2 of the Terminal Bases
The serial interface COM2 is not available at:
– Processor modules with type designator -2ETH (e. g. PM591-2ETH)
– Processor modules PM56xx
The serial interface COM2 is connected via a 9-pole D-sub connector. It is not intended to use
COM2 to establish a CS31 system bus. It is configurable for RS-232 or RS-485 and can be
used for
● online access
● a free protocol
● Modbus RTU, master and slave
If the RS-485 bus is used, each interconnected bus line (each bus segment) must be electrically
terminated. The following is necessary:
● 2 resistors of 120 Ω each at both line ends (to avoid signal reflections)
● a pull-up resistor at RxD/TxD-P and a pull-down resistor at RxD/TxD-N. These 2 resistors
care for a defined high level on the bus, while there is no data exchange.
System Assembly, Construction and Connection
AC500 (Standard) > Connection and Wiring
2019/04/173ADR010121, 13, en_US1280
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