My name is Taho. I have a BC7300 and 1 module KL3214 + end bus here. I'm trying to read data via Modbus from my laptop to BC using Modbus scan software. I had some issues with handshaking signal, which address of slave (BC7300) I should assign? Which modbus address of KL3214 i can read? Currently, RX led on BC7300 is ON, TX is OFF, do I need to program for BC7300 to send data via fieldbus?
Thank you so much, I'm looking forward to hear from you.
Hello Taho. Welcome to Control.com
Modbus is a master/slave protocol. A Modbus slave is silent, unless spoken to, at which point it responds with a reply message. A Modbus master always initiates communications. Unless the master is actively 'polling' a slave, the serial communications indicating LEDs will not show activity.
Your Modbus scan PC program is most likely a Modbus Master.
The master must be configured to:
- poll or query a specific slave (node) address
- use a Modbus Function Code to read data
- specify the register address where the data resides
- specify an address range or the number of bytes if the Function Code is capable reading multiple registers
On the Slave device, you need to know:
- that the device actually has Modbus slave functionality. Modbus is rarely referred to as a Fieldbus. Having either an RS-232 or RD-485 port does not mean that the device supports Modbus communications. If the documentation for the device does not mention Modbus, then it doesn't have Modbus functionality.
- which serial port Modbus uses
- which data is in which register on the slave device. For instrumentation, the manufacturer publishes a table or map of which data is where. Typically on a PLC, the PLC programmer moves data into specific registers.
- how to configure the Modbus slave address for the device
The serial settings need to be identical on both the master and the slave.
I can not help you on Beckhoff specifics, it's outside my experience.