Immediate Boolean - Automationdirect.com DirectLOGIC DL205 Series User Manual

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.
CPU Scan
X128
OFF
Read Inputs from Specialty I/O
Solve the Application Program
X0
Write Outputs to Specialty I/O
Chapter 5: Standard RLL Instructions - Boolean
X0 _ X10
X7 X17
e CPU reads the inputs from
Th
the local base and stores the
status
Read Inputs
register .
... X2 X1 X0
... ON OFF OFF
Input Image Register
Immediate instruction does
not use the input
register , but instead reads the
Y0
status
I
immediately.
Write Outputs
Diagnostics
DL205 User Manual, 4th Edition, Rev. B
X20 Y0 _ Y10 Y20
Y30
X30
_ _ _ _ _
_
X27 Y7 Y17 Y27 Y37
X37
in an input image
OFF
OFF
image
from the module
I/O Point X0 Changes
ON
OFF
X0
X1
X0
X1
5–9
1
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A
B
C
D