7 Modbus/TCP – SmartWire-DT implementation
7.5 Acyclic data communications
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SmartWire-DT Gateway EU5C-SWD-EIP-MODTCP
08/17 MN120003Z EN
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0x113F. This must be done within 30 seconds of writing to register 0x113E.
It is also possible to write to both registers with a single operation by using
function codes FC16 and FC23
7.5 Acyclic data communications
In addition to cyclic data, acyclic information can also be exchanged between
a Modbus-TCP master and a SmartWire-DT module. There are specific Mod-
bus registers and services for assigning requests and for receiving the
requested data for this purpose.
When acyclic services are used, the data is stored in these Modbus regis-
ters. The Modbus client will then wait until the request has been processed.
This is indicated by means of a request acknowledgment. Once this acknowl-
edgment is received, the response can be read. If acyclic communication
requests for various modules are being processed at the same time, the PLC
will manage them. The following table describes the detailed structure of
these register spaces.
Registers 8000h - 807Fh:
"Acyclic service objects, request space"
MODBUS register
Description
0x800C - 0x807F
Registers for request space
0x8080 - 0x80FF
Registers for response space
MODBUS register
Name
Data type
&Value
Description
0x8000
SERVICE NUMBER
UINT
0 - 0xFFFF
This register holds a user-specific value that is
deleted after the service is run.
The value is copied to the SERVICE NUMBER
register in the response space after the service is
run.
0x8001
0x8002 (Low Byte)
INDEX
USINT
0 -0xFF
The INDEX entry is used to specify the applica-
tion object.
Application objects are described in the "Smart-
Wire-DT Modules IP20", MN05006001Z.
0x8002 (High Byte)
SERVICE CODE
USINT
0 - 255
The SERVICE CODE entry is used to specify the
type of access:
0x00: NO FUNCTION
0x03: READ
0x10:WRITE
0x8003 (Low Byte)
DESTINATION
ADDRESS
USINT
0 - 99
Address of the SmartWire-DT module
0x8003 (High Byte)
SLOT
USINT
0
0 (not a modular Modbus module)
0x8004
LENGTH
USINT
0 - 120
Length of data to be read or written
0x8005 - 0x807F
OPTIONAL DATA
(Register 0 - 122)
UINT
0 - 0xFFFF
Object-specific data or error codes
