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How Block I/O Fits in a
PLC System
Block I/O is a complete I/O interface that includes the functionality of the
I/O rack, adapter, power supply, and I/O module in a single unit. Connect
sensors and actuators to the module and use the remote I/O cable to
connect the block I/O to your programmable controller.
Connect the block I/O to your remote I/O link as you would any other
device. Input and output data is scanned asynchronously and transferred
back and forth between the block and the programmable controller using
either block transfer or discrete transfer. When using block transfer
(Figure 1.2), the block looks like a 1/4 I/O rack to the processor (two
words of input image table memory and two words of output image table
memory). Block transfer provides the most efficient use of your data table
image memory, and allows access to all implemented user functions of
the block.
Figure 1.2
Block I/O Connection in a PLC System using block transfer
Programmable
Controller
or Scanner
Blocks are daisy chained to
a programmable controller or
a scanner
Chapter 1
Introducing Block I/O
Block I/O each block
is 1/4 I/O rack
1/4
1/4
1/4
+
+
1/4
+
= 1 I/O Rack
10828 I
1-3
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