Modbus Standard; Basics; Figure 4 Master Slave Query Response Cycle - ABB LVS Digital Manual

M OD BUS STA N DARD

2.2. Modbus Standard

MODBUS is a serial data communication protocol and was originally developed as a
communication language for MODICON programmable controllers, its rights now reside with
the Modbus-IDA organization.
The software on the Digital Gateway supports the pure Master-Slave operation as defined in
the MODBUS RTU specification. This manual describes the Digital Gateway communication
with MODBUS protocol in RTU and TCP modes.
The MODBUS communication protocol is implemented within the Digital Gateway to enable
LVS Digital to provide interface possibilities to process control systems or any other external
systems that supports MODBUS RTU / TCP protocol handling.
The MODBUS configuration can be used in point to point configuration or in multi-drop
mode. In Master-Slave MODBUS architecture, the Digital Gateway is always used in a slave
(TCP: Server) mode. The master station controls the traffic on the bus, in this case, by
PCS/DCS or PLC system. The Digital Gateway responds to the queries received from master
station as per the MODBUS specification.
.

Basics

Figure 4 Master Slave Query Response Cycle

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