Is a PLC a MODBUS slave?

MODBUS is a “master-slave” system, where the “master” communicates with one or multiple “slaves.” The master typically is a PLC (Programmable Logic Controller), PC, DCS (Distributed Control System) or RTU (Remote Terminal Unit). Slave devices on MODBUS networks cannot initiate communication; they can only respond.

Why is MODBUS used in PLC?

MODBUS is a commonly used industrial communications protocol. It allows the exchange of data between PLCs and computers. It was originally designed for Modicon (Schneider Electric) PLCs but has become widely used by many PLC manufacturers and industrial networks.

What are the working modes of MODBUS?

MODBUS SERIAL TRANSMISSION MODES Standard Modbus networks employ one of two types of transmission modes: ASCII Mode, or RTU Mode. The transmission mode defines the bit contents of the message bytes transmitted along the network, and how the message information is to be packed into the message stream and decoded.

How many devices can be connected to MODBUS?

Modbus is restricted to addressing 247 devices on one data link, which limits the number of field devices that may be connected to a Parent station (once again, Ethernet TCP/IP is an exception).

Is the PLC the master or slave?

A PLC master with a DCM interface connected to one or more PLC or DCM slaves is the most popular type of network. The PLC is the network master and uses the DCM to initiate all communication requests. The DCM or PLC slave stations respond to the master station requests for data.

What must be the same for all devices on a Modbus network?

The speed that Modbus messages are sent is known as the baud rate (or bits per second) and all devices on the network must use the same baud rate, typically 9,600-19,200 Baud, but network speeds as fast as 115 kb/s are not unknown.

What is the maximum number of devices that can be connected in RS485 communication using a repeater?

32 nodes
A: RS-485 devices can be connected to a computer and multi-dropped at various locations in a network style configuration. Devices can be up to 4000 feet (1220 meters) feet away before a repeater is needed, and up to 32 nodes (devices) can be connected.

Can Modbus have multiple masters?

Since Modbus TCP uses stateless connections, it is possible for two or more masters to write to the same register or coil in a Modbus device – and write different values.

Can 2 Masters Plcs control the outputs of 1 slave?

It is also possible to have two masters on profibus network, but I think that it has to be sure that one slave has to be connected to only one master or at least two or more master can only listen to slaves, but two masters cannot send data to one mastaer in one time..