Gem80 ESP protocol to modbus ESP- any suggestions (redlion maybe)?

We’ve been using a Gem80-142 to provide a serial link to a group of starter & drives for finfans and pumps for many years. The GEM80 uses port 1 on its ribbon cable to give serial information to the drives for remote start/ stop and running indication via an rs485 link.

Port 2 of the GEM80 ribbon cable needs to communicate to our DCS system (in this case Honeywell TDC3000) via a Data Hiway Port using the Modbus RTU protocol. The GEM80 uses ESP protocol, and this previously was wired through an rs422-current loop converter and then an ESP-Modbus converter. The ESP-Modbus converter acted as a Modbus Slave to the TDC system and as a master to the GEM80.

We had a big plant upset recently which was finally traced back to a wire shorting across the back off the RS422 to RS485 converter PCB. Prior to this, all Port 2 operation stopped.

The GEM80 has been checked over, tested etc and is fully functioning. Port 1 is functioning fine too. However we believe we've got a fault with the protocol converter. These are now obsolete.

I'm looking into finding a new system of converting the Modbus RTU protocol commands to ESP protocol instructions for the GEM80. The functions generally take the form of requests for the state of A or B table data in the GEM for DCS running indication, or write information to the B tables as start or stop signals.

It appears we can use the Data Station Plus for this application. However the only Drivers I can find for the GEM80 listed are for J/K table master or slave. Can these drivers be used to read/ write data from the A & B tables?

I've spoken to the Red lion tech support and they seem to have been helpful and said they'll get back, but I thought you guys may know how easy it would be or have another solution in mind?

PS Excuse the looooong first post, but I thought the more background the better.

There must be 100's of these honeywell to GEM80 systems in use (I worked on 2 or 3) so there should be an easy solution. Try the converteam customer support guys and see what they say.

J/K tables were reserved for serial link information, A/B tables were digital I/O. You just need to move the A/B's into the J/K's

As StarWatcher implied, the ESP protocol works by exchanging the J table in one device with the K table in the other, and vice versa. Each table can contain 32 words of information, if I remember correctly. Per StarWatcher, the way to handle comms is to move data to and from the J/K tables according to what you want to transfer. If you can get access to the GEM80's programming port, there is also a protocol that can randomly read and write other tables, but that might not be usable in your application.

I thought the same as both of you before this installation, but the gem80 A and B table addresses can apparently be accessed by the Protocol Converter somehow, I've attached the manual for the protocol converter as a .zip file, page 7 of the pdf (page 4 of the manual) says that it uses relocation constants in the P table (P55-P58) to map the Gem80 addresses for the Honeywell (modbus) addressing. Page 16 (page 13 of the manual) gives an example. In this case it all ties up with both the addresses displayed on the Honeywell system and the gem80 addresses I have in a listing of the variables. I checked the entire logic and there are no collate functions or anything used to move this data to the J/K tables.

Converteam checked the Gem80 and were as confused as I was as it shows nothing has ever been used in the J/K tables on port 2 (they therefore couldn't believe it ever worked). It must be able to retrieve data from the A,B,G&H tables, though I still don't know how.

We do have access to the programming port, but I guess if we use this we wouldn't be able to use the programming port to monitor the gem logic via a PC-based program at all in future?

No attachment...

Sorry missed the attach button first time.

The manual says it sends programming port messages, so I suspect the GEM is supporting that protocol on the ESP ports when configured as tribs. The relocation stuff is how it maps the data without needing any configuration -- it uses random reads to pick up the config from the PLC, and then fetches the data based on that information. I'd be fairly certain that our programming port protocol ought to be capable of doing what you need, but of course the config will then be in the DSP.

Ok it's all starting to come together now. The protocol converter is currently using an active current loop to a current-loop to rs422 converter to communicate back through the ribbon cable, I think we're going to get hold of a Cegelec (gem 80) rs422 to r485 converter to connect the ribbon cable into and give us an rs485 connection for the DSP.

The Data Station Plus went on order from one of your UK distributors yesterday, we're hoping to get it on-site next week and have a look at how we're going to configure it.