DL205 User Manual, 4th Edition, Rev. B
5–9
Chapter 5: Standard RLL Instructions - Boolean
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5
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A
B
C
D
Immediate Boolean
The DL205 Micro PLCs can usually complete an operation cycle in a matter of milliseconds.
However, in some applications you may not be able to wait a few milliseconds until the next
I/O update occurs. The DL205 PLCs offer Immediate input and outputs which are special
boolean instructions that allow reading directly from inputs and writing directly to outputs
during the program execution portion of the CPU cycle. You may recall that this is normally
done during the input or output update portion of the CPU cycle. The immediate
instructions take longer to execute because the program execution is interrupted while the
CPU reads or writes the I/O point. This function is not normally done until the read inputs
or the write outputs portion of the CPU cycle.
NOTE:
Even though the immediate input instruction reads the most current status from the input point, it
only uses the results to solve that one instruction. It does not use the new status to update the image
register. Therefore, any regular instructions that follow will still use the image register values. Any
immediate instructions that follow will access the I/O again to update the status. The immediate output
instruction will write the status to the I/O and update the image register.
X0
OFF
X1
OFF
CPU Scan
Read Inputs
Diagnostics
Input Image Register
Th
e CPU reads the inputs from
the local base and stores the
status in an input image
register .
X0
Y0
X0
X1
X2
...
X128
OFF
OFF
ON
...
OFF
Solve the Application Program
Read Inputs from Specialty I/O
Write Outputs
Write Outputs to Specialty I/O
X0
ON
X1
OFF
Immediate instruction does
not use the input image
register , but instead reads the
status from the module
immediately.
I/O Point X0 Changes
X0
_
X7
X10
_
X17
X20
_
X27
Y0
_
Y7
Y10
_
Y17
Y20
_
Y27
Y30
_
Y37
X30
_
X37
I
