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Programming Concepts Section 1-1
• An upwardly differentiated instruction (DIFU or @ instruction) will output
ON only when the execution condition is ON and flag for the previous
value is OFF.
• Use in Interlocks (IL - ILC Instructions)
In the following example, the previous value flag for the differentiated
instruction maintains the previous interlocked value and will not output a
differentiated output at point A because the value will not be updated
while the interlock is in effect.
• Use in Jumps (JMP - JME Instructions): Just as for interlocks, the pre-
vious value flag for a differentiated instruction is not changed when the
instruction is jumped, i.e., the previous value is maintained. Upwardly and
downwardly differentiate instructions will output the execution condition
only when the input status has changed from the status indicated by the
previous value flag.
Note (a) Do not use the Always ON Flag or A200.11 (First Cycle Flag) as
the input bit for an upwardly differentiated instruction. The instruc-
tion will never be executed.
(b) Do not use Always OFF Flag as the input bit for a downwardly dif-
ferentiated instruction. The instruction will never be executed.
1-1-10 Refresh Timing
The following methods are used to refresh external I/O.
• Cyclic refresh
• Immediate refresh (! specified instruction, IORF instruction)
Cyclic Refresh Every program allocated to a ready cyclic task or a task where interrupt condi-
tion has been met will execute starting from the beginning program address
and will run until the END(001) instruction. After all ready cyclic tasks or tasks
where interrupt condition have been met have executed, cyclic refresh will
refresh all I/O points at the same time.
Note Programs can be executed in multiple tasks. I/O will be refreshed after the
final END(001) instruction in the program allocated to the highest number
(among all ready cyclic tasks) and will not be refreshed after the END(001)
instruction in programs allocated to other cyclic tasks.
IL
0.00
ILC
DIFU
10.00
0.01
0.00
0.01
10.00
A
IL is
executing
IL is
executing
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