PM8000 the register 54396

[sesa12489_bridg]

In the registers table of the PM8000 we have the register 54395 dedicated to display if the configuration of the frequency is 50Hz or 60Hz.

If I read the this register in INT16 I got -1 (1111 1111 1111 1111 in binary).

It is normally 1 or 0 in INT16 why it is -1?

It is written that this register is in R/W and I tried to write 0 (50Hz) and I got a modbus exception answer code 512.

Should I need to use a protected command in the same way as PM5000 but it is not mentioned in the table of registers of the PM8000_Modbus_Map (excel file)

In the web page the configuration of 50Hz Vs 60Hz is working fine but the customer want to perform that through a com Modbus configuration.

Thanks for your help.