Balluff BIS M-62 Series, Manual

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DEVICENET INTERFACE
117
8
8.2.5 DeviceNet - Handshaking Example
This example describes the sequence of events for a simple command and response. All
data is written in 2-byte
WORD format and stored in 2-
byte “
registers.
”
The Output Controller Tag holds command data written by the PLC. The Input Controller
Tag holds response data generated by the Controller. Handshaking is implemented using the
first two words ( Words 0 and 1 ) in both Input Controller Tag and Output Controller Tags .
The PLC writes a command to the
Output Controller Tag , starting with the 2-byte Consume
Data Size value at Local:2:O.Data [2] (which is the third register of the Output Controller
Tag ). The remainder of the command packet is then written, 2-byte per register, to the
Output Controller Tag, starting at the fourth register, Local:2:O.Data [3]. After writing the
command packet data to the appropriate registers, the PLC increments the counter value
stored at
Local:2:O.Data [1] (the second register in the Output Controller Tag ).
The counter at
Local:2:O.Data [1] is copied by the Controller to Local:2:I.Data [0] (the first
register of the Input Controller Tag ) which signals the PLC that the command has been
received by the Controller.
Following execution of the command, the Controller writes its response to the
Input
Controller Tag, starting with the 2-byte Produce Data Size, at Local:2:I.Data [2] and the
actual data beginning at Local:2:I.Data [3] . It then increments the counter value at
Local:2:I.Data [1] . This alerts the PLC to the new data available (the Controller generated
response, in this case).
After processing the response information, the PLC copies the counter from
Local:2:I.Data
[1] to Local:2:O.Data [0] , which signals to the Controller that the PLC has retrieved the
response data.
OUTPUT CONTROLLER TAG
Controller Tag Location and
Data
Description
Local:2:O.Data [0]
(4) The PLC copies the value at 2:I:Data[1] here to acknowledge
receipt of the response
Local:2:O.Data [1]
(1) The PLC increments this counter value after copying a command
in Consume Data
Local:2:O.Data [2] Consume Data Size
Local:2:O.Data [3] First WORD of Consume Data ( Command from PLC )
Local:2:O.Data [xxx] xxx WORD of Consume Data