Does the MSTR block read 3x registers?
Yes, since the advent of Function Code 15 the MBP_MSTR can read 3x registers. This functionality is found on Unity processors.
The attached project in ZEF format contains an example of how to configure the MBP_MSTR with OpCode 15 to read 3x / 300000 / %IW registers from a server Modbus TCP device. This example was created with a double-wide Quantum CPU module, but the MBP_MSTR can be used in the same way with Momentum and M580 CPU modules. In the Data Editor, you will find the Control and Data Arrays. Read the comments section for each of the registers to see how they should be configured.