WEG CFW100 User Manual - page 19
Detailed Description of the Functions
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)
Response (Slave)
Slave Address
Slave Address
Function
Function
Address of the initial register (high byte)
Byte count
Address of the initial register (low byte)
Datum 1 (high)
Number of registers (high byte)
Datum 1 (low)
Number of registers (low byte)
Datum 2 (high)
CRC-
Datum 2 (low)
CRC+
etc...
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)
Response (Slave)
Field
Value
Field
Value
Slave Address
01h
Slave Address
01h
Function
03h
Function
03h
Initial register (high)
00h
Byte count
04h
Initial register (low)
02h
P0002 (high)
00h
Number of registers (high)
00h
P0002 (low)
1Eh
Number of registers (low)
02h
P0003 (high)
00h
CRC-
65h
P0003 (low)
0Fh
CRC+
CBh
CRC-
DAh
CRC+
31h
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)
Response (Slave)
Slave Address
Slave Address
Function
Function
Register address (high byte)
Register address (high byte)
Register address (low byte)
Register address (low byte)
Value for the register (high byte)
Value for the register (high byte)
Value for the register (low byte)
Value for the register (low byte)
CRC-
CRC-
CRC+
CRC+
Phone: 800.894.0412 - Fax: 888.723.4773 - Web: www.ctiautomation.net - Email: info@ctiautomation.net