Programming Overview
4–3
With the logic program entered into the controller, placing the controller in the
Run mode initiates an operating cycle. The controller’
s operating cycle consists of a
series of operations performed sequentially and repeatedly, unless altered by your
program logic.
input
scan
program
scan
output
scan
service
comms
overhead
Operating Cycle
input
scan
– the time required for the controller to scan and read all input data;
typically accomplished within µseconds.
program scan – the time required for the processor to execute the instructions in the
program. The program scan time varies depending on the instructions used and
each instruction’
s status during the scan time.
Note Subroutine
and interrupt instructions within your logic pr
ogram may cause
deviations in the way the operating cycle is sequenced.
output scan – the time required for the controller to scan and write all output data;
typically accomplished within µseconds.
service communications – the part of the operating cycle in which communication
takes place with other devices, such as an HHP or personal computer
.
housekeeping and overhead – time spent on memory management and updating
timers and internal registers.
You enter a logic program into the controller using a programming device. The
logic program is based on your electrical relay print diagrams. It contains
instructions that direct control of your application.
Programming
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