RS232 Serial Protocol Conversion


Thread Starter

Cheryl Muldoon

I need to convert 4 different RS232 serial protocols to a common format.

Our PLC only accepts messages ending in a CR or LF. Currently the 4 different RS232 serial protocols do not end in a CR or LF. Lastly, messages leaving the PLC need to have the CR and
LF removed.

Can anyone offer any advice as to how we might be able to achieve this?

Cheryl Muldoon
PLC Peripherals

Darold Woodward

While this may border on a commercial response, we have a solution you may be interested in. Some other manufacturers also offer similar devices. I'll describe how ours would work in your case.

One approach would be to use a communications processor. The idea is to collect the data on four ports that would be completely independent in terms of messaging, protocols, and even data
speeds. Then you can present the data to the other PLC as a single protocol interface. Our communications processor has a very flexible messaging system that is capable of emulating most
simple ASCII data collection and many binary protocols. You could also use DNP, Modbus, or Modbus Plus to send the data to the master.

If you have any questions about our device, please let me know. You can look at our device at

Darold Woodward PE
SEL Inc.
[email protected]
Sierra Monitor Corporation has a device with 8 serial ports, a library of already implemented serial protocols, a toolkit to allow users to add more protocols, and a service where we can implement additional protocols for you if you desire.

Please see our website,

Curt Wuollet

Hi Cheryl

An old 486 and a $2.00 Linux disk would make an unbeatable gateway if you understand the protocols. Linux and UNIX in general provide
unmatched flexibility in serial comms. I have a general skeleton program that opens ports, sets parameters etc. and after that it's simply read,
modify,write. For what you are doing, a shell script might even suffice as the ports can be setup for nl/nlcr , parity, speed, from the command line. A (relatively) cheap Rocketport board will get you 8 extra ports, and the inner workings of the serial driver are well documented and standardized. You can get the Rocketport board with RS4xx protos also. I do a lot of this sort of thing and it's stable, reliable, and you
know how it works so changes aren't a big deal.