Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 99)

Chapter 6
Programming Overview
6–2
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
µ
seconds.
program scan – the time required for the controller 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.
Important: Subroutine and interrupt instructions within your logic
program 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
µ
seconds.
service communications – the part of the operating cycle in which
communication takes place with other devices, such as a
MicroLogix 1000 HHP or a personal computer.
housekeeping and overhead – time spent on memory management and
updating timers and internal registers.