NMEA Sentence parsing in PLCs

[rajsiyer 7]

Hi fellow geeks, Many of us are using GPS.. In my recent project, I had to get GPS into SCADA. Easy it was, as the GPS port monitoring software (ASDLOG) has a DDE/OPC server + parsing features by which one may set up specific NMEA sentences ($GPGLL, $GPZDA etc..) for parsing. Doing this on a PC with parsing software is easy. And for PLCs, there are indeed converter devices which convert NMEA sentences into neatly arranged Modbus registers. My question however is.. Can we rig up a PLC's serial port (RS-422 is typical for GPS devices), and set up an ASCII buffer and then look into this ASCII data and pick out the Lat., Long. & time data? Has anyone done this?? I would like to know the method. Is the NMEA protocol mere ASCII and how would you enable the port to continuously receive the NMEA sentences.. assuming it is all in ASCII Thanks for looking in, best wishes

[lostcontrol 23]

I did this a couple of years ago with an Omron PLC, think it was a brick as well as a CJ2. I will have to check. All it was doing was reading data from the serial buffer, the GPS outputted a serial stream every 100ms that I read & split. I will try & find the code to refresh & post what I can.

[wal 0]

I did it with Mitsubishi FX3u. It seems worked, but the problem for me, was the cycle redundancy check (for tracking errors). Later I found better solution. In the Beijer T7A HMI there is option NMEA 0183 as an extra controller. Works fine. It saves the GPS data to PLC registers (it does not matter which PLC make). Then You can use the data anyway.

[rajsiyer 7]

Thanks Wal, But this time round, I am getting an embedded device which will parse the NMEA sentence and store it in generic modbus registers. I think it is only a matter of time before the GPS makers will give modbus registers as well. Wish you all the best.