Section 6 Wiring Serial interfaces of the CPU module
M&I – AC 900F Controller 91
The two 470 Ohm resistors are integrated into the CPU module and can be activated
by a short wire link between the terminals 1-2 and 3-4. The following drawing
shows an RS485 bus with a bus master at the line end.
RS 485 bus_us.png
If the master is located within the bus line, a terminating resistor is not provided.
The pull-up resistor and the pull-down resistor, however, need to be activated (see
drawing below). The cable shields of the bus line must be earthed.
RS-485 Bus_bus line_us.png
Ethernet_Connect_us.png
The external 120 ohm resistor (line termination) must be protected against
electrostatic discharge. It is recommended to provide the complete resistor
(except for the wire ends) with a heat shrink tube for this purpose.
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