Emerson PACSystems RX3i - Figure 21: RTU Read Output Table Example

PACSystems™ RX3i and RSTi-EP CPU Reference Manual Section 6
GFK-2222AK October 2019
Serial I/O, SNP & RTU Protocols 163
23
Read/Write 4x Registers
24–66
Unsupported Function
67
Read Scratch Pad Memory
68-127
Unsupported Function
128-255
Reserved for Exception Responses
6.3.1.5.3 Information Fields
All message fields, other than the Station Address field, Function Code field, and Error
Check field are called, generically, information fields. Information fields contain additional
information required to specify or respond to a requested function. Different types of
messages have different types or numbers of information fields. (Details on information
fields for each message type and function code are found in RTU Message Descriptions.
Some messages (Message 07 Query and Message 17 Query) do not have information
fields.
6.3.1.6 Examples
As shown in the following figure, the information fields for message READ OUTPUT TABLE
(01) Query consist of the Starting Point No. field and Number of Points field. The
information fields for message READ OUTPUT TABLE (01) Response consist of the Byte
Count field and Data field.
Figure 21: RTU Read Output Table Example
Address
Starting
Point No.
Number of
Points
Error
Check
Func
01
Information Fields
Query
Hi
Hi
Lo
Lo
Message (01)
Read Output Table
Address
Data
Error
Check
Func
01
Information Fields
Normal Response
Byte
Count
Some information fields include entries for the range of data to be accessed in the RTU
slave.