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TECHNICAL MANUAL
LARGE DISPLAYS DN109/NB - DN119/NB - DN189/NB - DN129/NB
CHAPTER 24
This section details how the information is structured at the protocol level in order to debug
communication problems with a MODBUS frame analyzer.
If you already have knowledge of this protocol, you can go directly to
it is explained how the information must be encapsulated in the records according to the type of
data that you want to represent, as well as the control characters that are available.
•
Read Coils: Allows to visualize the state of the internal bits or designated
physical Coils. The structure of this function is presented below:
Request
Function code
Start adress
Number of Coils
Answer
Function code
Number of bytes used
Coil status
Error
Error code
Exception code
Example:
The display only has the 2nd Coil active, to know the status of all of them you can use this function.
The following frames are sent and received:
IMPORTANT: Upon receiving the byte (02h) that indicates the status of the Coils, it should be
read as follows:
X
X
Table 61: Coils status reading. "X" indicates that it is not used or not relevant.
ETHERNET COMMUNICATION
1 Byte
2 Bytes
2 Bytes
1 Byte
1 Byte
n Bytes
1 Byte
1 Byte
Table 60: "Read Coils" function structure.
0
X
0
Coil #5
01h
0001h to 0005h
0001h to 0005h
01h
N (N = # Inputs / 8)
n = N o N+1
81h
01 or 02 or 03 or 04
2
0
0
Coil #4
Coil #3
24-3
section 24.2.2
where
1
0
Coil #2
Coil #1
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