Modbus RS-232 and Modbus RS-485

Modbus is a protocol that uses serial communication lines. These serial lines connect a Modbus master to “slave” devices along a Modbus network. A Modbus master can support up to 247 slave devices on one serial communication network.

Two Types of Modbus: Modbus RS-232 and Modbus RS-485
There are two different types of serial connection that Modbus can be transmitted over. These are RS-232 and RS-485.

Modbus RS-232 Allows Concurrent, Two-Way Flow of Data
Modbus RS-232 communications send data in the form of time-series of bits. It is a standard for communication between data terminal and data circuit-terminating equipment. Transmission and receipt for data occurs on different circuits when using Modbus RS-232 lines, allowing data to flow both ways at the same time. The range of voltages on RS-232 is related to one and zero values, creating the basis of the bit communications.

Modbus RS-485 Indicates Values Using Differences in Voltage
Modbus RS-482 is the Modbus protocol variant that uses an RS-485 connection. This two-wire, multipoint connection communicates data by indicating values by sending different voltages across the two wires. These differences between these voltages are related to one and zero values, which make up the Modbus R2-485 communications.

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Related Products:
T/Mon NOC

To see additional information related to a "Modbus HMI", please visit the Modbus page.

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