Super Systems AC20 RS485 Modbus - Manual (Page 9)

Page 9/59
TITLE: MODBUS/J-BUS Protocol for SSi’s- AC20 ENG. 824E REV. 1
Function code 6: Single word writing
By using this command, the master unit can change the value of one word (16 bit) of the
slave unit.
Command from master to slave Reply from slave to master
Range Byte Range Byte
Slave address (0*-255) 1 Slave address (1-255) 1
Function code (06) 1 Function code (06) 1
Word address (high byte) 1 Word address (high byte) 1
Word address (low byte) 1 Word address (low byte) n
Data 2 Data 2
Error check (CRC-16) (low byte) 1 Error check (CRC-16) (low byte) 1
Error check (CRC-16) (high byte) 1 Error check (CRC-16) (high byte) 1
* To use the address 0, see note 1 at page 12: “Broadcast address”.
The 8000h value, present in the “data” field, should be considered as a don’t care value,
that is, the value present in the device at this address will not be modified.
Example:
Set word 2006 (7D6h) of slave at address 5 (5h) with value 1250 (4E2h)
Command from master to slave Reply from slave to master
Range Byte Range Byte
Slave address 05h Slave address 05h
Function code 06h Function code 06h
Word address (high byte) 07h Word address (high byte) 07h
Word address (low byte) D6h Word address (low byte) D6h
Data 04h Data 04h
Data E2h Data E2h
Error check (CRC-16) (low byte) EAh Error check(CRC-16) (low byte) EAh
Error check (CRC-16) (high byte) 4Bh Error check (CRC-16) (high byte) 4Bh