DCP200 Profile Controller & Recorder -Product Manual
Page 80 Serial Communications 51-52-25-150, Issue 1 –April 2009
Supported Modbus Functions
Modbus defines several function types. The following types are supported by this instrument:
Function Code
(decimal)
Modbus Meaning
Description
03 / 04 Read Holding/Input registers Read current binary value of specified number of
parameters at given address. Up to 64 parameters
can be accessed with one Query.
06 Write Single Register Writes two bytes to a specified word address.
08 Diagnostics Used for loopback test only.
16 (0x10 hex) Write Multiple Registers Writes up to 253 bytes of data to the specified
address range.
23 (0x17 hex) Read/Write Multiple Registers Reads and Writes 253 bytes of data to the specified
address ranges.
Function Descriptions
The following is interpreted from the Modbus Protocol Description obtainable from
http://www.modbus.org/. Refer to that document if clarification is required.
In the function descriptions below, the preceding device address value is assumed, as is the
correctly formed two-byte CRC value at the end of the QUERY and RESPONSE frames.

Function 03 / 04 - Read Holding/Input Registers

Reads current binary value of data at the specified word addresses.
QUERY
Function
Address of 1
st
Word
Number of Words
03 / 04 HI LO HI LO
R
ESPONSE
Function
Number of
Bytes
First Word
Last Word
03 / 04 HI LO HI LO
In the response the “Number of Bytes” indicates the number of data bytes read from the
instrument. E.g. if 5 words are read, the count will be 10 (A hex). The maximum number of
words that can be read is 64. If a parameter does not exist at one of the addresses read,
then a value of 0000h is returned for that word.