TimD
Lifetime Supporting Member
Hello,
I have a DirectLogic 260 PLC that I want to read modbus data into and issue commands to field devices.
Right now, there is a CMore HMI that is the master, and it reads the information from the field devices for trending only.
My questions are:
1. "Who" should the Master be, and Why?
2. If the PLC needs to be the master, can it be in the middle of the modbus network, or does it need to be at one end and terminated with a resistor? (PLC is located near one end of the chain, but not at the end.
3. My network is RS485 3-wire (A, B, GND) but the PLC has an 8-wire connection (TXD2 +/-, RTS2 +/-, RXD2 +, CTS2 +/-, GND) available. Do I just use the TXD + and - lines, plus GND?
Thanks,
Tim
I have a DirectLogic 260 PLC that I want to read modbus data into and issue commands to field devices.
Right now, there is a CMore HMI that is the master, and it reads the information from the field devices for trending only.
My questions are:
1. "Who" should the Master be, and Why?
2. If the PLC needs to be the master, can it be in the middle of the modbus network, or does it need to be at one end and terminated with a resistor? (PLC is located near one end of the chain, but not at the end.
3. My network is RS485 3-wire (A, B, GND) but the PLC has an 8-wire connection (TXD2 +/-, RTS2 +/-, RXD2 +, CTS2 +/-, GND) available. Do I just use the TXD + and - lines, plus GND?
Thanks,
Tim
Last edited: