Super Systems AC20 RS485 Modbus - Manual (Page 11)

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TITLE: MODBUS/J-BUS Protocol for SSi’s- AC20 ENG. 824E REV. 1
Function code 16: Multiple words writing
This function code is used by the master unit to write a consecutive group of words .
The master unit can change a maximum of 20 words at a time.
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 (16) 1 Function code (16) 1
Word starting address (high
byte) 1 Word starting address (high byte) 1
Word starting address (low byte) 1 Word starting address (low byte) 1
Number of words (high byte) 1 Number of words (high byte) 1
Number of words (low byte) 1 Number of words (low byte) 1
Byte counter (n) 1 Error check (CRC-16) (low byte) 1
Data n Error check (CRC-16) (high byte) 1
Error check (CRC-16) (low byte) 1
Error check (CRC-16) (high byte) 1
* To use the address 0, see note 1 at page 12: “Broadcast address”.
The data imposed for read only words will be ignored.
The command will be processed starting from the first word and it will be executed or not
executed depending on the actual device status.
At the first error found, the command will be aborted and the slave will answer with an
error.
The 8000h value, present in the “data” field, should be considered as a don’t care value,
this is, the value present in the device at this address will not be modified.
Example:
Set words 139 (8Bh), 140 (8Ch), 141 (8Dh) of slave at address 10 (Ah) with 300 (12Ch),
don’t care (8000h) and 700 (2BCh) values.
Command from master to slave Reply from slave to master
Range Byte Range Byte
Slave address 0Ah Slave address 0Ah
Function code 10h Function code 10h
Word starting address(high byte) 00h Word starting address (high byte) 00h
Word starting address (low byte) 8Bh Word starting address (low byte) 8Bh
Number of words (high byte) 00h Number of words (high byte) 00h
Number of words (low byte) 03h Number of words (low byte) 03h
Byte counter 06h Error check (CRC-16) (low byte) F1h
Data 01h Error check (CRC-16) (high byte) 59h
Data 2Ch
Data 80h
Data 00h
Data 02h
Data BCh
Error check (CRC-16) (low byte) 33h
Error check (CRC-16) (high byte) 00h