Immediate Boolean - Automationdirect.com DL05 User Manual

Chapter 5: Standard RLL Instructions

Immediate Boolean

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The DL05 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
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I/O update occurs. The DL05 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
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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
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writes the I/O point. This function is not normally done until the read inputs or the write
outputs portion of the CPU cycle.
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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
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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.
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a A
B b
C c
D D
5-8 DL05 Micro PLC User Manual, 6th Edition, Rev. D
CPU Scan
Read Inputs
X11 ... X2 X1
OFF ... ON OFF
Input Image Register
Read Inputs from Specialty I/O
Solve the Application Program
X0 Y0
I
Write Outputs
Write Outputs to Specialty I/O
Diagnostics
The CPU reads the inputs from the local
base and stores the status in an input
image register.
X0
ON
OFF
OFF
Immediate instruction does not use the
input image register, but instead reads
the status from the module immediately.
ON
OFF
X0
X1
I/O Point X0 Changes
X0
X1