CPU Specifications
and Operation
4–14
CPU Specifications and Operation
Input Update
Result of Program
Solution
OFF
Image Register (example)
Y1Y2
...Y128
ONON...OFF
C0C1C2...C377
OFFOFFON...OFF
Y0
OFF
X1X2...X128
ONON...OFF
X0
Bit Override OFF
Force from
Programmer
Input Update
Result of Program
Solution
Bit Override ON
Force from
Programmer
WARNING: Only authorized personnel fully familiar with all aspects of the
application should make changes to the program. Make sure you thoroughly
consider the impact of any changes to minimize the risk of personal injury or damage
to equipment.
There are certain V-memory locations that contain Special Relays and other
dedicated register information. This portion of the execution cycle makes sure these
locations get updated on every scan. Also, there are several different Special
Relays, such as diagnostic relays, etc., that are also updated during this segment.
The CPU evaluates each instruction in the
application program during this segment
of the scan cycle. The instructions define
the relationship between the input
conditions and the desired output
response. The CPU uses the output
image register area to store the status of
the desired action for the outputs. Output
image register locations are designated
with a Y followed by a memory location.
The actual outputs are updated during the
write outputs segment of the scan cycle.
There are immediate output instructions
available that will update the output points
immediately instead of waiting until the
write output segment. A complete list of
the Immediate instructions is provided in
Chapter 5.
The internal control relays (C), the stages
(S), and the variable memory (V) are also
updated in this segment.
Read Inputs
Solve the Application Program
Write Outputs
Diagnostics
Update Special Relays
Service Peripherals
Normal Run mode scan
You may recall that you can force various types of points in the system. (This was
discussed earlier in this chapter.) If any I/O points or memory data have been forced,
the output image register also contains this information.
Update Special
Relays and Special
Registers
Solve Application
Program
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