KB89480
Published: April 16, 2021
Revision: 3.0

OptoMMP Server Resets When Writing to Modbus/TCP Holding Register(s) with Unit ID Greater Than 1


Applies To:

Firmware for:

  • GRV-EPIC-PR1
  • GRV-R7-MM1001-10

Versions Affected:

GRV-EPIC-PR1: All versions prior to 3.2.0
GRV-R7-MM1001-10: All versions

Resolved In Version:

GRV-EPIC-PR1: 3.2.0


Symptoms:

When using Modbus/TCP to write to Holding register(s) with Unit ID greater than one on a groov EPIC I/O unit or groov RIO unit, the OptoMMP server will reset.  This will cause the groov I/O or RIO unit to temporarily go offline.  It will recover automatically.

Workaround:

Use a Unit ID of 1 and determine the appropriate starting Holding Register number using the information under the HOLDING REGISTERS topic in Chapter 3 of the ​Modbus/TCP Protocol Guide (form 1678).

Or you can use a Unit ID of 1 and calculate the appropriate starting Holding Register number by using this formula: register_address = 1031 + <slot_number>*(64*2) + <channel_number>, where:

  • slot_number is the slot number on the groov EPIC chassis (remember that the numbering begins with 0).
  • channel_number is the channel number on the module (remember that the numbering begins with 0).

For example, to set the analog output value for channel 0 on the module in slot 2, write 2 holding registers starting at address 1031 + 2*64*2 + 0 = 1287.

Resolution:

Opto 22 has resolved this issue and will include the fix in an upcoming release.

Questions?

Contact: Opto 22 Product Support.
Phone: 800-835-6786 or 951-695-3080
Email: support@opto22.com


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