Rockwell Automation DEVICENET 1771-SDN, User Manual

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Publication 1771-6.5.132 - June 2000
Before You Begin 1-7
Communicating with Your
PLC-5 Processor
Your processor communicates with the 1771-SDN scanner module via
block transfer reads, block transfer writes , and DIO transfers.
Input data, gathered from the network’s devices, is organized within
the 1771-SDN and made available for the processor to “read”.
The 1771-SDN module does not send data to your processor.
Data transferred between the module and the processor must be
initiated by the processor.
Output data is sent, or “written”, to the
scanner by your processor. This data is organized in the 1771-SDN
module, which in turn passes the data on to your scanned devices via
strobe, poll, change of state, or cyclic messages.
A block transfer read (BTR) is
a block transfer of data from
the 1771-SDN module to the
PLC processor. The processor
is
reading the data collected
by the 1771-SDN module
(i.e., DeviceNet input data).
A block transfer write (BTW)
is a block transfer of data
from the PLC processor to
the 1771-SDN module. The
processor is
writing the data
to the 1771-SDN’s memory
(i.e., DeviceNet output data).
PLC-5 Processor
1771-SDN Scanner
B
A1
C
D
A2
E
E
X
Y
Y
Z
Y
Y
C
D
A2
X
Z
Y
Y
Y
Y
Discrete Input Image
Block Transfer Data File
A1
B
E
E
Internal Input
Data Storage
I/O Map
Input from
the devices
Discrete Output Image
Block Transfer Data File
Internal
Output Data
I/O Map
Discrete I/O
Transfer
Block
Transfer
Write
Discrete I/O
Transfer
Block
Transfer
Read
Output to
the devices