Hi Joe,
I hope our R&D will read the topic and will take notes. Meantime - small tip:
You can use module "Struct". This module will arrange diferent data types, from different places to one MI vector. I know it's not exactly what you aske about, but in case you want to read/write diferent operands, from different areas, this can simplify sensitivelly the program and, for me even more important - will spead very much the communication. As Modbus is "handshake protocol and each command request confirmation, usually reading 10 registers in one command is much faster than rea"d two registers one by one.