Serial Communications
RS-485 Termination and Biasing
Termination - Proper RS-485 termination minimizes reflections and improves reliability.
The MJ2 serial port allows 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.
This termination is only in place when the Micro OCS Controller is powered on. This would typically only be an issue
if the Micro OCS Controller is being used as a slave on the RS485 network. In that case, the electronic should not
be used, but a physical external termination resistor should be used instead.
Biasing - RS485 biasing passively asserts a line-idle state when no device is actively transmitting, which is useful
for multi-drop RS485 networking. The MJ2 serial port allows internal bias resistor to be activated by software con-
trol, pulling pin 1 up to 3.3V and pulling pin 2 down to ground.
NOTE: 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.
Biasing Details:
n
%SR152.3 enables RS485 Port Termination
n
%SR164.1 enables RS485 Port Biasing
Cscape Programming via Serial Port
MJ1 is the serial port available for programming. The connection is RS-232 and is compatible with the Horner pro-
gramming cable kits HE-XCK or HE-XCPK. Unlike some other OCS models, the MJ2 port cannot be configured as
a programming port. The Mini-B USB port is also available for programming.
The “Set Serial Ports” option in the OCS System Menu contains an entry for Default Programming Port (Dflt Pgm
Port). However, the entry is fixed at MJ1-232. No OCS configuration is required to use either the MJ1 serial port or
Mini-B USB port for programming. NOTE: Only one Cscape software connection is allowed at a time.
Page 97 of 163
To Next Page
Loading...