Toshiba T2N User Manual download pdf (Page 233)

5. Programming Language

220 PROSEC T2N

The following shows the concept of the execution system in one SFC

program.

(1) In one scan, evaluation of the transition condition, the step

transition processing and the execution of the action program unit are

sequentially operated.

(2) Evaluation of the transition condition means the execution of the

transition condition connected to an active step and carrying out a check

for transition condition establishment. At this time, since evaluation is

made only for active step, there are no multiple step transitions by 1

scan in consecutively connected steps.

(3) Step transition processing means making the previous step

inactive and the following step active if the transition condition is

satisfied, based on the result of evaluation of the transition condition.

(4) Execution of the action program unit corresponding to the active

step is carried out by switching the power rail ON, and executing the

action program unit corresponding to the inactive step by switching the

power rail OFF. At this time, as shown in the following diagram, the

execution sequence is from top to bottom, and from left to right in

branches.

The numerals in the diagram show

the execution sequence of the

action programs.

Execution System

For instance, as shown in the diagram on the right, in

a program in which the transition condition from step

100 to 101 and the transition condition from step 101

to 102 are the same, step 100 becomes active in the

previous scan, and when device A has been switched

ON in the present scan, there is transition to step 101

in the present scan. (Transition to step 102 will be from

the next scan onward)

1 2 ... 228 229 230 231 232 233 234 235 236 237 238 ... 271 272

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Toshiba T2N User Manual Page 233