MAN1106-07-EN_XL+_UserManual
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10.4 RS485 Termination and Biasing
Proper RS485 termination minimizes signal reflections and improves reliability.
MJ1, MJ2, and MJ3 serial ports allow an internal termination resistor to be placed across pins 1
and 2 by software control.
Only the two devices physically located at the endpoints of the RS485 network should be
terminated.
RS485 biasing passively asserts a line-idle state when no device is actively transmitting, which
is useful for multi-drop RS485 networking.
MJ1, MJ2, and MJ3 serial ports allow internal bias resistor to be activated by software control,
pulling pin 1 up to 3.3V and pulling pin 2 down to ground.
If biasing is used, it should be enabled in only one of the devices attached to the RS485
network.
The “Set Serial Ports” option in the OCS System Menu can be used for termination and
biasing. Also, an application graphics screen that writes to %SR can do the same thing. Below
are the details:
•
For MJ1 termination make high %SR152.3
•
For MJ2 termination make high %SR152.1
•
For MJ3 termination make high %SR152.2
•
For MJ1 biasing make high %SR152.4
•
For MJ2 biasing make high %SR164.1
•
For MJ3 biasing make high %SR164.2
10.5 Cscape Programming via Serial Port
The XL+ OCS MJ1, MJ2, and MJ3 serial ports support CsCAN Programming Protocol. If a PC
COM port is connected to the XL+ OCS MJ1, MJ2, or MJ3 serial port, Cscape can access the
XL+ OCS for programming and monitoring. Programming can also be done via the CAN port,
USB A ports, or Ethernet.
10.6 Ladder-Controlled Serial Communication
Using Serial Communication function blocks, MJ1, MJ2, and MJ3 serial ports support Generic
Modbus Master and Modbus Slave Protocols. In addition, external modems can be connected
and accessed using Modem function blocks.
