MODBUS Cheatsheet

Master

Master Gateway

Slave Gateway

Slave

Address Data Mapping

Knows all Slaves' IDs and the data they can provide

Contains a list of all Slaves' IDs and their WAN addresses (IP/Port)

Contains a list of all local Slave IDs and their LAN addresses

Contains Register and Coil Data

Local Transfer Protocol

Preconfigured to know how to communicate with each other.

• ”Serial RTU”

• “Serial ASCII”

Preconfigured to know how to communicate with each other.

• ”TCP”

• ·“Serial RTU”

• “Serial ASCII”

WAN Encapsulation (Over the Air Transfer Protocol)

No knowledge

Preconfigured to know how to communicate with each other. “TCP” or “RTU over UDP”

No knowledge

Data Conversions

Gateways will convert data from ASCII to RTU to and vice-versa to satisfy its respective “Local Transfer Protocol” as well as “WAN Encapsulation”