Despatch Protocol 3 Modbus Communications - Manual (Page 11)

Modbus Programming Manual A BOUT T HIS M ANUAL
Version 2 11
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Function 23 Hex - Read / Write Multiple Registers (0x17 hex)
Reads and writes the requested number of consecutive words (two-bytes) starting at the specified
addresses.
QUERY
Function 1 st Read
Address
Number of
Words to
Read
1 st Write
Address
Number of
Words to Write
Values to Write
1 st Word 2 nd Word etc Last Word
17 HI LO HI LO HI LO HI LO HI LO HI LO → HI LO
RESPONSE
Function Number of Bytes Read Data
1 st Word 2 nd Word etc Last Word
17 HI LO HI LO → HI LO
Note:
The number of data bytes that can be read and written in one message is 253 bytes.
Exception Responses
When a QUERY is sent that the instrument cannot interpret, an Exception RESPONSE is
returned. Possible exception responses are:
Exception Code Error Condition Interpretation
00 Unused
None.
01 Illegal function Function number out of range.
02 Illegal Data Address Write functions: Parameter number out of range or not
supported. (for write functions only).
Read Functions: Start parameter does not exist or end
parameter greater than 65536.
03 Illegal Data Value Attempt to write invalid data / required action not executed.
The format of an exception response is:
RESPONSE
Function Exception Code
Original Function code with its Most
Significant Bit (MSB) set. as detailed above
Note:
In the case of multiple exception codes for a single QUERY the Exception code returned is
the one corresponding to the first parameter in error.