Delfino DRH7, User Manual

Page: 9 / 16

Protocol
5
About Modbus RTU overview:
The electrode acts as a slave on the network and supports the Modbus RTU
communication protocol.
Data communication is initiated by the host, and the first byte of the transmitted message
is the target slave address. After the first byte is received by all the slaves on the network,
each slave will decode it to determine whether the message is sent to itself.
The transmission of the RTU message frame shall start with a pause interval of at least
3.5 character time. After the transmission of the last character, a pause of at least 3.5
characters time marks the end of the message frame. A new message can start after this
pause. During transmission, the entire message frame must be transmitted in a
continuous stream. If there is a pause interval of more than 1.5 character time before the
transmission of the message frame is completed, the receiving device will flush the
incomplete message and assume that the next byte is the start of a new message.
Likewise, if a new message begins with the previous frame within less than 3.5
characters, the receiving device will consider it a continuation of the previous frame, and
this will result in an error because the final CRC The value cannot be correct.
The host can send command frames to read individual or all data results.
The data frame format is as follows (all data are in Hex format)
Host sends:
1 2 3 4 5 6 7 8
slave
address
function
code
Register start
address upper
8 bits
Register
start
address
lower 8 bits
The upper
8 bits of the
number of
registers
The lower 8
bits of the
number of
registers
CRC
lower 8
bits
CRC
high 8
bits
The slave responds:
1 2 3 4 5 5+n 5+n+1 5+n+2 5+n+3
slave
address
function
code
Data
bytes
Data 1
high 8
bits
Data 1
lower 8
bits
Data n
high 8
bits
Data n
lower 8
bits
CRC
lower 8
bits
CRC
high 8
bits
Chapter 4 Communication
4.1 About Modbus RTU Overview