Horner APG XLt OCS - Manual (Page 24)

CH. 5 MAN0878-04-EN
August 12, 2009 Page 24 of 100 ECN # 979
5.4
RS-485 Termination
Proper RS-485 termination minimizes reflections and improves reliability.
Both serial ports allow an internal 121-Ohm RS-485 termination resistor to be placed across pins 1 and 2.
This can be done by installing a jumper. Please refer to the XLe/XLt data sheet for jumper locations.
In any case, only the two devices physically located at the endpoints of the RS-485 network should be
terminated.
5.5
RS-485 Biasing
RS-485 biasing passively asserts a line-idle state when no device is actively transmitting, which is useful
for multi-drop RS-485 networking.
Both serial ports allow internal 390-Ohm RS-485 bias resistors to be switched in, pulling pin 1 up to 3.3V
and pulling pin 2 down to ground. The Set Serial Ports item in the System Menu (see page 51) can be
used to enable RS-485 biasing. Also, an application graphics screen that writes to %SR164 can do the
same thing. Setting %SR164.1 enables MJ1 biasing and setting %SR164.2 enables MJ2 biasing.
If biasing is used, it should be enabled in only one of the devices attached to the RS-485 network.
5.6
Cscape Programming via Serial Port
The XLe/XLt MJ1 serial port supports CsCAN Programming Protocol, but MJ2 does not. If a PC COM
port is connected to the XLe/XLt MJ1 serial port, Cscape can access the XLe/XLt for programming and
monitoring.
5.7
Ladder-Controlled Serial Communication
Using Serial Communication function blocks, both MJ1 and MJ2 support Generic, Modbus Master and
Modbus Slave Protocols. In addition, external modems can be connected and accessed using Init, Dial
and Answer Modem function blocks.
5.8
Downloadable Serial Communication Protocols
Both MJ1 and MJ2 also support downloadable protocols, such as Allen Bradley DF1, CsCAN Master, GE
Fanuc SNP and Modbus Master.