Do-more plc modbus ascii protocol will be used to communicate to a Solo process temperature controller. A sample program will explain in detail how this is accomplished through a serial port.
Modbus is a communication method used for transmitting information over serial lines between electronic devices. The device requesting the information is called the Modbus Master (Client) and the devices supplying information are Modbus Slaves (Servers). This protocol was originally developed by Modicon systems.
Modbus protocol comes in basically three different types. Ethernet (Modbus TCP) or Serial (Modbus RTU or Modbus ASCII). Modbus TCP and Modbus RTU come as standard protocols in the BRX Do-More series of PLCs.
We will connect the BRX Do-More PLC to a Solo process temperature controller. This will be done using the Modbus ASCII protocol over serial RS485 communication wire. (Media) The present and set values (PV / SV) will be read from the Solo controller and the set value will be written when required. Let’s get started. Continue Reading!
We will be looking at the Modbus remote IO BX-MBIO-M controller. This is the Do-More Modbus Remote I/O supported protocol unit. We will discuss the hardware and then connect and configure the unit to work with our existing BRX Do-more PLC. Let’s get started.
The BX-MBIO Modules are remote I/O controller modules that provide a remote input and output (I/O) using the Modbus protocol for communications. They provide both Modbus RTU and Modbus TCP interface. Modbus RTU is a serial communication and Modbus TCP is an Ethernet communication. They function as listening/replying devices (slave, server) and can connect with any mastering (master, client) device that communicates using the Modbus protocol.
Modbus RTU is supported over an RS-485 serial connection. Modbus TCP is supported over an Ethernet connection. Any Modbus RTU master and Modbus TCP client that adheres to the Modbus.Org standards, and support the function codes listed can communicate with the BX-MBIO. The remote I/O expansion units feature the following:
• RJ45 Ethernet port for communications via Modbus TCP
• RS485 serial port for communications via Modbus RTU
• Supports up to 8 additional Expansion Modules (Add the discrete or analog I/O you require)
• AC and DC powered units available
• AC powered units include an integral 24VDC auxiliary output power supply
• Power connector and serial port connector included
Recently I was asked to demonstrate communication between a BRX PLC and Click PLC using Modbus RTU. Both PLCs are available from automation direct com. Modbus serial communication (Modbus RTU) is a standard protocol used in many automation devices. It works on a Master / Slave configuration. You can have only one master per network on Modbus RTU (Remote Terminal Unit). A maximum of 32 devices (Nodes) on the network can communicate to the master. A review of the Modbus RTU protocol (RTU frames) can be seen at the following URL. http://www.rtautomation.com/technologies/modbus-rtu/
Using the BRX PLC as a Master, we will be communicating to the Click PLC (Slave). Our example will read 10 registers from the Click PLC and write 10 registers from the BRX PLC. Let’s get started! Continue Reading!