86
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 23 Hex - Read / Write Multiple Registers (0x17 hex)
Func
Code
1st Read
Address
Number of
Words
1st Write
Address
Number of
Write Words
Byte
Count
Values to Write
1st Word
etc
Last Word
17
HI
LO
HI
LO
HI
LO
HI
LO
XX
HI
LO
g
HI
LO
QUERY: Function 23 Hex - Read / Write Multiple Registers (0x17 hex)
Func
Code
Byte
Count
1st Word
etc
Last Word
17
XX
HI
LO
g
HI
LO
Note: The maximum number of data bytes that can be read and written in one message is 253 bytes.
Exception Responses
If a QUERY is sent without a communication error, but the instrument cannot interpret it, an Exception RESPONSE
is returned. The exception response consists of a modified version of the original function code and an exception
code that explains what was wrong with the message. Possible exception responses and their reasons are:
Function Code
Exception
Code
Modbus
Meaning
Description
The original function
code with its most
significant bit (MSB) set.
This offsets it by 0x80,
so for example 0x06
becomes 0x86.
00
Unused
None
01
Illegal
Function
Function number is out of range.
02
Illegal Data
Address
Write functions: Parameter number is out of range
or not supported. (for write functions only).
Read Functions: Start parameter does not exist or
the end parameter greater than 65536.
03
Illegal Data
Value
Attempt to write invalid data / required action not
executed.
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.
Modbus Parameters
The register addresses for the Modbus parameters are
detailed in the tables below. The Access column indi-
cates if a parameter is read only (RO) or if it can also
be written to (R/W). Communications writes will not be
implemented if the Writing Via Serial Comms param-
eter in the Communications Configuration sub-menu is
set to Disabled.
Data Formats
Data can be accessed in three formats: Integer Only
(decimal places are not included), Integer with 1 Deci-
mal Place (only the first decimal place value is includ-
ed) or an IEEE / Motorola (big endian) Floating Point
Number. Where possible use floating point numbers
especially if the values have more than one decimal
place.
Note: Read only parameters will return an excep-
tion if an attempt is made to write values to them.
Some parameters that do not apply for a particu-
lar configuration will still accept read / writes (e.g.
attempting to scale a linear output which has not
been fitted).
Summary of Contents for Chromalox 4081
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