Micromod Micro-DCI: 53MC5000 PLC AND PRINTER INTERFACES - Manual (Page 65)

6.0 MODBUS RTU MODE
6.1 PURPOSE
The Modbus Remote Terminal Unit (RTU) interface application permits data transfers between the
Process Control Station (PCS) and an addressed Modbus Programmable Logic Controller (PLC).
The Modbus RTU binary protocol, with a given command set for initialization, write, read, and diag-
nostics is supported by the PCS. All of the Modbus command messages are followed by a Longitu-
dinal Redundancy Check (LRC). The PCS can operate as a Modbus master or a slave. PCS
Modbus master operation is described first in this section followed by PCS Modbus slave operation.
6.2 INSTALLATION CONFIGURATIONS
Typical point-to-point and multidrop Modbus installation configurations are illustrated in Figures 6-1
and 6-2 respectively. In the multidrop configuration, communication is bidirectional with one node;
however, the read and write functions can be separated across two PLCs if necessary.
PCS Modbus Master Point-to-Point Installation
PCS Modbus Slave Point-to-Point Installation
Figure 6-1. Typical Modbus Point-to-Point Installations
53MC5000
PCS
MASTER
RS-232/485
ITB MODBUS
PLC
53MC5000
PCS
SLAVE
RS-232/485
ITB MODBUS
HOST
Multidrop
Figure 6-2. Typical Modbus Master Multidrop Installation
53MC5000
PCS
MASTER
RS-232/485
ITB MODBUS
PLC
MODBUS
PLC
(TO BE READ)
(TO BE WRITTEN)
RS-485
Section 6. MODBUS RTU Mode
MODBUS2
6-1