Knowledge Base / Rockwell In-chassis / ControlLogix / MVI56 Series

MVI56-MCM

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What is the difference between the MVI56-MCM and the MVI56-MCMR?

The MVI56-MCM is our general purpose Modbus serial (RTU and ASCII are supported) master/slave solution for ControlLogix, and is the preferred choice when used in the local chassis with the controller, or in a remote chassis via Ethernet.The MVI56-MCMR communicates across the back...

When I increase the ReadData or WriteData array sizes in my program, all of the configuration parameter values go to 0.

When controller tag array sizes are changed in the ControlLogix platform, RSLogix5000 re-initializes all of the tags within that data type. This sets all values to 0 in all tags within that group. Before changing any controller tag array sizes, the user should record all configur...

What causes a conditional command to be issued?

A conditional command is useful when the same value does not need to be written to the end device continuously, but rather on change. A conditional write command is scanned based upon its poll rate (like all other commands). The difference is that it will not be execut...

How to configure more than 100 commands per port when using an MVI46-MCM, MVI69-MCM, or the MVI56-MCM as a Modbus master?

Master command list contains up to 100 individual entries. Event command control blocks may be used to send additional Modbus commands directly from theladder logic to one of the master ports....

What is the purpose of the UseGuardBand/GuardBandTime or InterCharacterDelay parameters in an MCM module?

Due to timing variations in various Modbus devices, it is possible for a Modbus master to have problems sending write commands to the MCM slave port while having no issues with read commands.In such cases, the "Use Guard Band" and "Guard Band Time" parameters ...

I was not using both Modbus ports on my MVI56-MCM module, so I set all the port parameters for the unused port to zeros to disable the port and now my module is faulted and will not restart. Why?

On some older modules, setting the baud rate to zero for either Modbus port will cause the entire module to fault. Modbus ports on the MVI56 can be individually enabled or disabled using the controller tag mcm.portx.enabled, where x=the port number in the controller tags mcm tabl...

Where are the on-board jumper positions defined for my MVI module?

On bottom of the circuit board for any MVI products, you' ll find three jumper banks: COM1, COM2, and Setup.Each jumper position is labeled 232, 422 and 485....

Apparent data corruption in 33 words of MVI56-MCM or MVI56E-MCM ReadData or WriteData arrays.

In your controller tags, if MCM.Config.ModDef.ErrStatPtr is 0, then status data is likely overwriting the first 33 words of the MCM's ReadData or WriteData arrays which would typically be used for Modbus data.Enter a value of -1 for this variable if status information isn't being...

Do the serial ports on my MVI56 module provide any electrical isolation?

The two application serial ports provide 1000 volts of electrical isolation between the port and the ControlLogix backplane.The debug/configuration port provides no electrical isolation. Note: None of the ports provide any electrical isolation between the port and the module's i...

How can I configure the module to store and initialize input values on reset or powerup?

You can initialize the input data (ReadData) with cached values from the processor on these In-Chassis modules so that these values do not get reset to 0 during a module reset or powerloss. To do this the parameter labeled "Initialize Input Image" or "Initialize Ou...

How to avoid slow data updates on a Modbus network with an MVI56(E)-MCM or MVI69-MCM when some Slaves are either not on-line or not functioning correctly?

A customer wrote: "Prosoft Modbus communication modules for Allen Bradley, like MVI56-MCM, experience timeout problems and polling delays on RS-485 multipdrop networks if slaves are powered off or faulty. For example, if we have 10 slaves communicating on the...

How do I increase my ReadData array for an MVI56-MCM module?

The sample ladder file must be modified in 3 locations. Before making these changes, save the work you have already done, as changing this array, may erase any values in your MCM array.1. "MCMmoduledef" user defined object. open the user-defined object for "mc...

Bulletin 1-5165141 MVI56-MCM getting intermittent communications errors when operating on both ports

Version 1.26 of the MVI56-MCM module firmware has been created to address this issue. This new version of code uses interrupt timing, to drop the RTS line as quick as possible, and enable the module to be ready to receive messages as fast as it can. All previous versions of the m...

How can I enable/disable slaves using block 3000/3001?

Please refer to the user manual which explains the use of block 3000/3001. mci56-mcm_mcm_expanded_v8.acd, contains the needed part of the ladder touse this function....

Where is the configuration for the MVI56(E)-MCM?

The MVI56(E)-MCM is configured via controller scoped tags that are automatically generated when the rung of ladder is imported into RSLogix 5000. This rung of ladder also contains the AOI that is used to transport data back and forth to the MVI56(E)-MCM module. ...