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Thread: Learn Modbus - eZee Guide
November 19th, 2013, 10:04 PM #1ZUDD Guest
Learn Modbus - eZee Guide
What is Modbus?
Modbus is an Industrial Protocol Standard and this protocol is defined as a Master/Slave protocol.
Master/Slave means - a device operating as a Master will Poll one or more Devices operating as a Slave. This means a Slave device cannot volunteer information and it must wait to be asked for it.
- The master will Write data to a Slave device’s registers, and Read data from a Slave device’s registers.
- A register address or register reference is always in the context of the slave’s registers.
Modbus ASCII and Modbus RTU are simple Serial Protocols that use EIA-232 or EIA-485 to transmit data packets. The protocol defines function codes and the encoding scheme for transferring data as either single points (1-bit, coils) or as 16-bit data registers. This basic data packet is then encapsulated according to the protocol specifications for Modbus ASCII, RTU, or TCP.
ModbusTCP The TCP version of Modbus follows the OSI Network Reference Model; however the serial implementations of Modbus do not. Modbus/TCP defines the presentation and application layers in the OSI model. ModbusTCP makes the definition of Master & Slave less obvious because Ethernet allows Peer-to-Peer communication. The definition of client and server are better known entities in Ethernet based networking. In this context, the slave becomes the server and the master becomes the client. There can be more than one client obtaining data from a server. In Modbus terms, this means there can be multiple masters as well as multiple slaves. Rather than defining master and slave on a physical device by device basis. System designer responsible to create logical associations between Master and Slave Functionality.
Last edited by ZUDD; November 19th, 2013 at 10:27 PM.
November 19th, 2013, 10:32 PM #2ZUDD Guest
Modbus - Do you know?
- about Physical Connection
- about Registers Mapping?
- about Communication Parameters?
Last edited by ZUDD; November 20th, 2013 at 02:07 PM.