RS232C to MODBUS Interface


Thread Starter


Dear All,
I am new entrant to this forum. I need to interface Flow Totalizer that sends information on 3 wire RS232C serial port to MODBUS protocol. This hardware-software should be able to accept commands from Master. This STAND ALONE Unit should be addressable and parameters remotely programmable.

All are requested to help me out.
You need to provide a couple more bits of information to clarify. RS232 and Modbus aren't mutually exclusive, they're talking about two different characteristics like "dog" and "brown". In fact it's quite common for Modbus to be operated on an RS232 connection. Maybe your device is already using Modbus protocol or can be configured to do so.

But, if you already understand that point, then your post sounds as if your device is talking in some manufacturer-specific protocol, perhaps in ASCII.

If that's the case, and your device or its protocol is very common, there may be protocol bridges available (say from Prosoft Technologies) that will use that protocol on one side and connect to a Modbus network on the other side.

Failing THAT, you'll have to make a bridge yourself from scratch. A good candidate for this would be a small PLC with little or no I/O and two serial ports. You write the custom protocol and communicate with your device on one port, and store the values written to or read from the device in the PLC memory. Then your other port (even Ethernet if you want) can be a Modbus master or slave (and you won't have to write this because many PLC's already talk Modbus off the shelf).
It isn't a Modbus master you're looking for, it's some other set of functions relating to what you're going to do with the data.

You need to define what you need the software (that has a Modbus master) to do with the data from the flow totalizer.

Save it? Print it? Trend it? Make up billing invoices? Compare today's with last year's total on this date? Whatever . . .

When you've defined what you need to do, then you can shop for the appropriate software/hardware package or integration service that can perform those tasks.

HMI, SCADA, DCS software all do different things at different sophistication levels with a flow total and associated data. All those software packages have some means of communicating via the Modbus protocol.