36
Precautions Section 1-2
Using Execution Results from Differentiated Instructions
With differentiated instructions, execution results for instructions are reflected
in Condition Flags only when execution condition is met, and results for a pre-
vious rung (rather than execution results for the differentiated instruction) will
be reflected in Condition Flags in the next cycle. You must therefore be aware
of what Condition Flags will do in the next cycle if execution results for differ-
entiated instructions to be used.
In the following for example, instructions A and B will execute only if execution
condition C is met, but the following problem will occur when instruction B
picks up execution results from instruction A. If execution condition C remains
ON in the next cycle after instruction A was executed, then instruction B will
unexpectedly execute (by the execution condition) when the Condition Flag
goes from OFF to ON because of results reflected from a previous rung.
In this case then, instructions A and B are not differentiated instructions, the
DIFU (of DIFD) instruction is used instead as shown below and instructions A
and B are both upwardly (or downwardly) differentiated and executed for one
cycle only.
Note The CP1H CPU Units support instructions to save and load the Condition
Flag status (CCS(282) and CCL(283)). These can be used to access the sta-
tus of the Condition Flags at other locations in a task or in a different task.
Incorrect
Use
Condition Flag
Example: =
Instruction B
Instruction A
Reflects execution results for instruction
A when execution condition is met.
Reflects execution results for a previous
rung in the next cycle.
Previous rung
Correct
Use
Previous rung
Instruction A
Instruction B
Reflects instruction A execution results.
Condition Flag
Example: =
To Next Page
Loading...
