mvi69mcm

can anyone plz help me out to use mvi69mcm module

I'm sure there are many who could help if you asked them specific questions and gave some clues as to where you are in your understanding and where you need to get to.

Thanks DIR..

So based on the other thread you re-awoke, you have a Prosoft MVI69-MCM module is a Compact Logix rack with an 1769-L43 processor. You are trying to communicate to a MyCom Mypro CP-IV compressor using Modbus-Rtu via the 9pin RS485 port on the Prosoft card.

Although Prosoft seems to indicate terminating resistors are optional, I find it hard to agree. I would install a 120ohm terminating resistor at both ends of the communication line. You need to investigate if the CP-IV has an internal resistor built in.

I tried to download the CP-IV manual, but apparently the manufacturer didn't see fit to make it available on their website. Always be wary when a small operation like this does their own modbus implementation. The standard itself is confusing and it is often misunderstood and butchered.

So lets get into the details:

Can we assume that the PLC and CP-IV are the only two devices on your RS485 network?

How long is the distance between the PLC and the CP-IV?

What kind of cable did you use? Is it a twisted pair? 2 or 3 wire? Shielded? How was the shield terminated?

What are your communication settings. (baud rate, parity, start bits, stop bits, etc)

What modbus function calls does the CP-IV support?

Do you know what addresses you are trying to access? Do you have a map of their address structure?

Are you looking at all 16 bit data, or is some of it 32 bit?

Do you know if you need to do a word swap? (MSW_LSW or LSW_MSW)

Is there anything else of relevance you think we should know about?

And while your at it, let us know what version of RSLogix5000 you are using and what the firmware rev is on the Prosoft card.

Distance b/w mvm and cpIV is approx 20 metre
cable i am using is 4 core shielded.twisted pair and shield is grounded on both the terminations(on terminal SG at CPIV and on terminal 5 at nine pin connector of prosoft)
comm setting is as baud rate 19200,parity:none,data bit:8,stop bit:1
CPIV supports FC 3 and 6
address to access i do have
i am looking for 16 bit data
i dont need a word swap process

most of the times i get an error -11 which says request timeout for which i increased the timeout time in my mvi69mcm module configuration.
i am using rslogix5k v18 and prosoft v 2.24

i am really very depressed as it has taken far more time than i could have ever expected.
plz help me with this

Can you post a link to the manual for the CP-IV or a link that it can be downloaded from?

You say most of the time you get error -11. Does that mean some of the times it works, or just that some of the times you get a different error.

Did the manual recommend terminating the shield in the fashion that you did? From my standpoind, that is worst case scenario. You have taken the shield (antena) and dumped all that noise into your signal commons.

Make sure your 2 data wires are a twisted pair. Those shold be the two wires you put your 120ohm resistor across. Use one wire or both of the other wires in the other twisted pair to run your common if desired. Unhook the shield from one end and terminate it directly to chassis ground on the other end.

If the CP-IV supports it, try starting at 9600 baud first. The slower the baud rate the more stable the comms will be. You can always bring it back up once you have everything working just fine.

So your using FC03 Read Holding Registers and FC06 Write Single Holding Register?

Are you sure your not using FC16 Write Holding Registers instead of FC06?

Are you getting the (-11) error for both reads and writes?

Give us an example of some of the registers you are accessing in the control.

vijay singh said:

most of the times i get an error -11 which says request timeout for which i increased the timeout time in my mvi69mcm module configuration.

Click to expand...

It's unlikely that the device is taking too long to respond and changing the timeout will solve it. When I've seen this error code it usually means that the devices are not communicating at all.

Check that the jumpers in the MCM are set for RS-485 rather than RS-232.

Check that the port on MCM is set as the master, and that the slave has the correct node address for the command you are sending.

Try sending a simple command to read a single register before asking for more.

You could try swapping the TX and RX. Different manufacturers label their terminals inconsistently.

If you are struggling with the MCM, a useful test is to check that it can read itself:

Set up port 1 as the master and port 2 as the slave, and try to read some data. You can connect P1 & P2 with an ordinary ethernet cable. You should be able to use RSLogix to set values in MCM.Data.WriteData and see them MCM.Data.ReadData.

Once you have this working, you can be confident that you understand the MCM well enough to be able to make requests to other devices.

If you understand the Modbus message structure, you can use the MCM diagnostics to view the messages being sent and received.

This is not a complete trouble-shooting guide, more a collection of tips that I have found useful. I hope it helps.

- Ian

Thanks very very much to DIR and Ian S,i wouldn't be able to communicate with my slave devices had you all not helped me.

I have the manual of MVI69MCM which i can give to you all if you require,my email id is [email protected].

DamianInRochester said:

Although Prosoft seems to indicate terminating resistors are optional, I find it hard to agree.

Click to expand...

I have been to one site where the only way to get the Modbus working was to REMOVE the terminating resistor!

With the resistor fitted, some of the devices would drop out. It was bizarre.

That case wasn't involving an MCM though.

vijay singh said:

Thanks very very much to DIR and Ian S,i wouldn't be able to communicate with my slave devices had you all not helped me.

I have the manual of MVI69MCM which i can give to you all if you require,my email id is [email protected].

Click to expand...

Curious what your issue ended up being?

Ian S said:

I have been to one site where the only way to get the Modbus working was to REMOVE the terminating resistor!

With the resistor fitted, some of the devices would drop out. It was bizarre.

That case wasn't involving an MCM though.

Click to expand...

Hi Ian, I have never experienced that myself, but nothing suprises me anymore. In this case it would make me wonder if the devices themselves didn't already have the terminating resistor on board and nobody realized it.