7.10 Examples
The following examples illustrate various Modbus RTU commands. If an error occurs, please refer to the Exception Codes section.
7.10.1 Read Coil Status (01 HEX)
Description
This function reads the ON/OFF status of discrete outputs (coils) in the frequency converter. Broadcast is never supported for reads.
Query
The query message specifies the starting coil and quantity of coils to be read. Coil addresses start at zero, i.e. coil 33 is addressed as 32.
Example of a request to read coils 33-48 (Status Word) from slave device 01:
Field Name Example (HEX)
Slave Address 01 (frequency converter address)
Function 01 (read coils)
Starting Address HI 00
Starting Address LO 20 (32 decimals) Coil 33
No. of Points HI 00
No. of Points LO 10 (16 decimals)
Error Check (CRC) -
Response
The coil status in the response message is packed as one coil per bit of the data field. Status is indicated as: 1 = ON; 0 = OFF. The LSB of the first data
byte contains the coil addressed in the query. The other coils follow toward the high order end of this byte, and from ‘low order to high order’ in subsequent
bytes.
If the returned coil quantity is not a multiple of eight, the remaining bits in the final data byte will be padded with zeros (toward the high order end of
the byte). The Byte Count field specifies the number of complete bytes of data.
Field Name Example (HEX)
Slave Address 01 (frequency converter address)
Function 01 (read coils)
Byte Count 02 (2 bytes of data)
Data (Coils 40-33) 07
Data (Coils 48-41) 06 (STW=0607hex)
Error Check (CRC) -
NB!
Coils and registers are addressed explicit with an off-set of -1 in Modbus.
I.e. Coil 33 is addressed as Coil 32.
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