Detailed Description Of The Functions; Function 03 - Read Holding Register; Function 06 - Write Single Register - WEG CFW100 User Manual

6 DETAILED DESCRIPTION OF THE FUNCTIONS

A detailed description of the functions available in the CFW100 frequency inverter for the Modbus RTU is
provided in this section. In order to elaborate the telegrams it is important to observe the following:
The values are always transmitted in hexadecimal.

The address of a datum, the number of data and the value of registers are always represented in 16 bits.

Therefore, it is necessary to transmit those fields using two bytes – superior (high) and inferior (low).
The telegrams for request, as well as for response, cannot exceed 64 bytes.

The transmitted values are always integer, regardless of having a representation with decimal point. Thus,

the value 9.5 would be transmitted via serial as being 95 (5Fh). Refer to the CFW100 parameter list to
obtain the resolution used for each parameter.
6.1 FUNCTION 03 – READ HOLDING REGISTER
It reads the content of a group of registers that must be necessarily in a numerical sequence. This function has
the following structure for the request and response telegrams (each field represents a byte):
Request (Master)
Slave Address
Function
Address of the initial register (high byte)
Address of the initial register (low byte)
Number of registers (high byte)
Number of registers (low byte)
CRC-
CRC+
Example: reading of the motor speed (P0002) and the motor current (P0003) of slave at address 1 (assuming
that P0002 = 30 Hz and P0003 = 1.5 A).
Address: 1 = 01h (1 byte)

Initial register address: 2 = 0002h (2 bytes)

Value of the fist parameter: 30 = 001Eh (2 bytes)

Value of the second parameter: 15 = 000Fh (2 bytes)

Request (Master)
Field
Slave Address
Function
Initial register (high)
Initial register (low)
Number of registers (high)
Number of registers (low)
CRC-
CRC+
6.2 FUNCTION 06 – WRITE SINGLE REGISTER
This function is used to write a value for a single register. It has the following structure (each field represents a
byte):
Request (Master)
Slave Address
Function
Register address (high byte)
Register address (low byte)
Value for the register (high byte)
Value for the register (low byte)
CRC-
CRC+
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Detailed Description of the Functions
Response (Slave)
Slave Address
Function
Byte count
Datum 1 (high)
Datum 1 (low)
Datum 2 (high)
Datum 2 (low)
etc...
CRC-
CRC+
Response (Slave)
Value Field
01h Slave Address
03h Function
00h Byte count
02h P0002 (high)
00h P0002 (low)
02h P0003 (high)
65h P0003 (low)
CBh CRC-
CRC+
Response (Slave)
Slave Address
Function
Register address (high byte)
Register address (low byte)
Value for the register (high byte)
Value for the register (low byte)
CRC-
CRC+
Value
01h
03h
04h
00h
1Eh
00h
0Fh
DAh
31h