How do you unlock the Classic using modbus?

[RossW]

In order to unlock the classic you must write the unit's serial number to registers 0x7001 and 0x7002. This is done as follows:

For this example the serial number will be: 0x12345678

0x7001 = MSB(Serial number)  [0x1234]
0x7002 = LSB(serial number)   [0x5678]

Note that these registers are "MODBUS" 1-indexed, your actual write-multiple registers command packet will use 0x7000 and 0x7001.

Just for the pedantic amongst us who get confused by terms being used differently in different places...

Most documentation refers to the registers in decimal, and most use the term "Register" (including midnite in their modbus documentation) as the "outside" number and use the term "Address" for the actual wire-level value.

Thus "addresses"  0x7000 and 0x7001 would be generally known as "registers" 28672 and 28673 (and are shown as such in the midnite modbus doc)

Unfortunately, and contrary to the post above - WRITING to these registers over ethernet doesn't work.
You need to write to registers 20492/20493 (if using ethernet anyway).