Hitachi CP-X200 Instruction Manual page 250

Data:
A function command is set here.
The data format used in the X200 series is corresponding to the Modbus data format
below.
Name of Data
Coil Binary data that can be referenced and changed ( 1 bit long)
Holding Register 16-bit data that can be referenced and changed
Function code:
Specify a function you want to make the inverter execute. Function codes available to
the X200 series are listed below.
Function Code
0 1 h Read Coil Status
0 3 h Read Holding Resistor
0 5 h Write in Coil
0 6 h Write in Holding Register
0 8 h Loopback Test
0 F h Write in Coils
1 0 h Write in Registers
Error check:
Modbus-RTU uses CRC (Cyclic Redundancy Check) for error checking.
The CRC code is 16-bit data that is generated for 8-bit blocks of arbitrary length.
The CRC code is generated by a generator polynomial CRC-16 (X16+ X15+ X2+ 1).
Header and trailer (silent interval):
Latency is the time between the reception of a query from the master and transmission
of a response from the inverter.
3.5 characters (24 bits) are always required for latency time. If the latency time
shorter than 3.5 characters, the inverter returns no response.
The actual transmission latency time is the sum of silent interval (3.5 characters
long) + C078 (transmission latency time).
Maximum data size
Function (bytes available
per message)
Description
Maximum number of
data elements available
per message
4 32 coils (in bits)
4 4 registers (in bytes)
1 1 coil (in bits)
1 1 register (in bytes)
4 32 coils (in bits)
4 4 registers (in bytes)
B − 7
B 7