Rockwell Automation T6200 Compressor Anti-Surge and Capacity Controller - Manual (Page 192)

Modbus Interface – RS-232/RS-485
B-2
MODBUS Interface – RS-232/RS-485
Preface
The MODBUS communication link permits the T6200 to converse with DCS/SCADA systems
from other vendors or to interface data from a variety of PLCs. The T6200 can act as either a
MODBUS master or slave. In the master mode, the T6200 can accommodate up to 2500 PLC
points. This interface is a standard T6200 feature which does not require any special hardware or
software.
The standard RS-232 or RS-485 electrical interface, COMM2, is used between the
communucation ports for Modbus devices. The serial interface operates in the half-duplex mode
at a selectable data rate from 2400 to 38,400 bits per second.
IMPORTANT NOTE: Although the T6200 supports the RS-485 signal levels
(electrical interface), the software drivers on the communications ports of the T6200
do not support addressing of multiple devices. Hence, if the RS-485 mode of
operation is selected, care should be taken to ensure that only one other device (in
addition to the T6200) is connected on the communication link.
T6200 MODBUS Functions Supported
The following T6200 Modbus functions are supported:
01 Read Discrete Output Status. Obtains current status (ON-OFF) of a group of discrete outputs.
02 Read Discrete Input Status. Obtain current status (ON-OFF) of a group of discrete inputs
03 Read Setpoints, Analog Outputs, Loop Auxiliaries, Alarms, etc. Obtain current binary value in
any group of holding registers.
04 Read Analog Input Values. Obtain current binary value in any group of input registers.
05 Modify Discrete Output Status. Force Discrete Outputs to a state of ON or OFF.
06 Modify Analog Values. (Register Groups) Place a specific binary value into a register.