Modbus Standard; Basics; Figure 3 Master Slave Query Response Cycle - ABB M101 Manual

M O D B U S STA ND A R D

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 MNS Digital Gateway supports the pure Master-Slave operation as
defined in the MODBUS RTU specification. This manual describes the MNS Digital Gateway
communication with MODBUS protocol in RTU and TCP modes.
The MODBUS communication protocol is implemented within the MNS Digital Gateway to
enable MNS 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 MNS 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 MNS Digital Gateway responds to the queries received from
master station as per the MODBUS specification.

2.2.1. Basics

Figure 3 Master Slave Query Response Cycle

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