MULTI GAUGE CONTROLLER
COMMUNICATION
. .
FUNCTION CODES
The function codes have -byte length. These are instructions for Slave devices describing action
to be executed.
The following function codes are supported through the MG device.
FUNCTION CODE
FUNCTION
x
Read n-words
x
Write word
x
Write n-words
Table . : Modbus protocol function codes
It is recommended to use the x function to read data, and the x function to write. It applies
also to logic data. Other function codes are supported to ensure compatibility with the Modbus
documentation. Exchange of information between the Master and Slave devices is executed through
data words. These data consist of parameters. The de initions of individual words for the MG are
presented in tables, starting from . . .
Communication frame formats for individual function codes are described below.
. . .
x
- READ N-WORDS
It enables sequential reading of a number of parameters within one query.
It is necessary to de ine the address of the irst parameter and number of words to be read after
this address.
Query:
Device
address
Function
code x
First word address
Number of words to
read
CRC
byte
byte
MSB LSB
MSB LSB
MSB LSB
The maximum number of read words is
. The irst two bytes are the data for the irst parameter
( irst MSB in organisation). The subsequent byte pairs are the data for the following parameters.
Response:
Device
address
Function
code x
Number of
read bytes
Value of irst
word
...
Value
of
last word
CRC
byte
byte
byte
MSB LSB
...
MSB LSB
MSB
LSB
Example:
Read vacuum value and status of IG gauge.
Query:
TX:
CB
Response:
RX:
A
F
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