1-8
Here is an example of a response to the query given earlier:
Field Name Example (Hex)
Slave Address 11
Function Code 23
Byte Count Hi 00
Byte Count Lo 0C
Data Hi (Register 40108, First Read) 02
Data Lo (Register 40108, First Read) 2B
Data Hi (Register 40109, First Read) 00
Data Lo (Register 40109, First Read) 00
Data Hi (Register 40110, First Read) 00
Data Lo (Register 40110, First Read) 64
Data Hi (Register 40108, Second Read) 02
Data Lo (Register 40108, Second Read) 2B
Data Hi (Register 40109, Second Read) 00
Data Lo (Register 40109, Second Read) 00
Data Lo (Register 40110, Second Read) 00
Data Lo (Register 40110, Second Read) 64
Error Check (LRC or CRC) --
Function Code 23H Example (Response)
The contents of Register 40108 are shown as the two-byte values of 02 2B Hex or 555 Decimal.
The contents of Registers 40109 - 40110 are 00 00 and 00 64 Hex or 0 and 100 Decimal.
1.8.2:
Function
Code
42H
-
Encapsulated
DNP
for
LAN/WAN
QThe existing interface between the Network Card and the Main Unit is in Modbus RTU protocol. In
order to maintain all of the existing functionality, it is necessary to pass DNPover IP requests and
the resultant responses inside a Modbus wrapper.
DNP has commands of variable length, producing responses of variable lengths. A variable size
Modbus request that returns a variable size Modbus response requires a new, non-standard function
code 42H.
The creation of different DNPassociations over IP requires informing the Main EPM device when a
new association is made. Function code 42H requests include a bit to indicate TCP(0) or UDP (1),
the Client IPAddress, the UDP orTCP Client Port, and a bit to indicate if this is a New
Association (1) or a continuation of the Existing Association (0).