Compactlogix and 4 x Altivar 61 on modbus

Disclaimer: I'm in over my head here

Hi, I'm trying to establish a 2 wire modbus connection between 4 Telemecanique altivar 61 VFD's as slaves and a compactlogix L32E as master. I need to read some data from the drives: speed reference, frequency reference, amps and such and I need to be able to control the frequency reference and to be able to start/stop.

On my desk I have one ATV and the compactlogix connected via an 1761-NET-AIC. Between the CL and the net-aic I have a 1761-CBL-PM02 cable and between the ATV and the net-aic I have 2 wires: A-A and B-B, on the net-aic side I have wired A-Term and a terminating resistor on the ATV side.

I have set up the ATV communication, speed ref. and cmd. channel 1 to modbus, and I have followed the CIG-AP129A-EN-P publication from RA's knowledgebase on how to copy the tasks, UDT's and tags from the modbusmaster.acd file.

In my sample program I have set the following:

Mod_Active 1
Mod_Cmd_Number 1
Mod_Commands[0].Enable 1
Mod_Commands[0].SlaveAddress 1
Mod_Commands[0].FunctionCode 4
Mod_Commands[0].StartingAddress 9001 (Acceleration time in the ATV, it's supposed to read "30")
Mod_Commands[0].NumberofPoints 1

When running this none of the communication LED's on the CL or the net-aic lights up, and in the Modbus_Interface > Program Tags > Mod_Status[0].Functioncode I get "-2" wich is an errorcode meaning "Command is not sent because the number of bits
exeeds 320 or arry limits in the Master were exeeded."

I then changed Mod_Data_arry_Max from 250 to 10000 and now the communication lights are blinking and the MsgCountRec and MsgCountTrans are almost match each other like they are supposed to (MsgContRec was 0 before), but I still don't get any data and Mod_Commands[0].EchoReceived wich is supposed to equal Mod_Commands[0].Enable is 0 and I get a minor fault saying
"Arithmetic overflow. Result of an aritmetic instruction out of range." The errorcode in Mod_Status[0].Functioncode is now -124 wich I don't get at all.

Lowering the Mod_Data_arry_Max to under 10000 I get the same errors as when it was 250.

Setting Mod_Data_arry_Max to 10000 I feel that I have gotten some kind of communication running, but it just leads to alot of other problems, so I'm not sure if it's right or wrong.

I know that this isn't very well explained, but it's hard as I am not excatly sure what I'm doing.
I hope that somebody that has done this before is able to help me.

Regards

Simple answer: Buy a Prosoft.

They're designed to do the job, alot faster and generally all round are the best way to make any Logix PLC talk Modbus.

Yeah I know, but my boss talked to our RA Rep who told him that it could be done this way. So here I am.

Then call the RA rep and have him come and do it.

I hate it when sales people sell something that 'sort of kinda' works because theyre not the people that have to actually MAKE it work.

Leave array sizes as is, change Mod_Commands[0].AddressOffsetinMaster instead.
I beleive you need to put -9000 to get data in Mod_Data_InpReg3[0]
This will read register 39001 (based on command 4)
You may play with offset value - I don't remember if you put negative or positive number, but you got the idea.

Thanks for the reply, I see what you mean, but it doesn't quite do it.

Putting in 9000 gives me error code "-2" meaning that it sends but doesn't receive.

Putting in -9000 gets the MsgCounts going again but still gives the controller fault and the "-124" error code, and the EchoReceived is still 0.

I've played alittle with the addresses, but it's still the same.