2. Controller Architecture and Program Operation GEM80-400
Page 2-2 ALSPA GEM80-400 SERIES CONTROLLERS TECHNICAL MANUAL Issue 3 04/99
Figure 2.1 - GEM
80-400 Controller Module Architecture
2.2.
Operation Cycle
The controller operation can be divided into three separate phases:
•
a start-up procedure (Initialisation),
•
an operating cycle (Operating Phase),
•
a fault shut-down procedure (Error Handler).
The start-up procedure includes checking the controller (self-test) and compiling
of the user program and, on satisfactory completion, allows the system to be run.
The second phase is the operating cycle proper, where the controller inputs and
outputs data based upon the user program and plant information. The third
phase is dependent upon the continual self-checks carried out by the controller
or on the detection of a system fault. In the event of a fault, the controller enters
a fault shut-down phase and is designed to shut down in an orderly fashion. Figure
2.2 shows the operating cycle in more detail
The cycle time may be either undefined, in which case the program free runs and
repeats as soon as it can, or it may be preset to a regular defined interval. If a
repetition interval has been set which is shorter than either the program execution
time or the I/O scan time, the repetitive cycle will not be regular and the
controller free runs. The output scan is the first item in the cycle. If a regular
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