Modbus Converter connected in Multidrop Daisy Chain
Modbus Converter connected in Multidrop Daisy Chain
(OP)
Hi Guys,
I am designing a redundant UPS System. For Each UPS module I am providing a Modbus Device to communicate with the DCS system. But my client wants me to loop these Modbus devices in Multidrop Daisy Chain configuration, so that they only have to use one Port at the DCS side, which I have already done. But now they are planning to use 2 ports at the DCS end, but at the same time they want to communicate with both the modules from each port at the DCS side. Is it Possible to provide redundant signal after Multidrop Daisy Chain looping?
Thanks
Manu
I am designing a redundant UPS System. For Each UPS module I am providing a Modbus Device to communicate with the DCS system. But my client wants me to loop these Modbus devices in Multidrop Daisy Chain configuration, so that they only have to use one Port at the DCS side, which I have already done. But now they are planning to use 2 ports at the DCS end, but at the same time they want to communicate with both the modules from each port at the DCS side. Is it Possible to provide redundant signal after Multidrop Daisy Chain looping?
Thanks
Manu





RE: Modbus Converter connected in Multidrop Daisy Chain
Depending on the DCS you might be able to connect the two DCS Modbus master ports to the same network. In order to do this, you will need to be able to completely disbale one or the other of the ports under program control.
The process goes Port A is primary and port B is secondary. Port A is enabled and polling the UPS devices. Port B is disabled. Communication failures are detected on Port A and the decision is made to switch to port B. Port A is disabled, Port B is enabled and polling resumes on Port B.
RE: Modbus Converter connected in Multidrop Daisy Chain
RE: Modbus Converter connected in Multidrop Daisy Chain
RE: Modbus Converter connected in Multidrop Daisy Chain
Thanks for your help
Manu
RE: Modbus Converter connected in Multidrop Daisy Chain
RE: Modbus Converter connected in Multidrop Daisy Chain
Every device on a daisy chained RS485 or RS422 modbus network appears the same in the idle state. All the devices go to a tri-stated mode where they are just listening.
It makes no sense to connect the redundant slave ports to the same wiring. If (when?) a node fails and shorts the buss you have no redundancy. Every slave that is active and will respond needs it's own address, even if it's the same device with 2 ports.
The difference between a master and a slave is that a master will initiate communications and a slave will only respond to a communications request. So, you can put 2 master connections as long as only one is working at a time.
I suppose you can have both master ports use the same address as long as one is left tri-stated and does not do anything while the other one is communicating. You could also have 2 slave ports at the same address as long as only one is active at a time.
If you have 2 slave ports on each device and 2 master ports on the DCS then run 2 RS485 networks.