Hitachi NT2021XA, Instruction Manual

Page: 28 / 84

Chapter 2 Syntax
- Processing cycle
Refer to the statement execution sequence indicated by parenthesized numbers in the comment fields of the sample programs
below.
(1) :
The “for” line is executed only once.
(2) and (3) : <instruction set> is executed.
(4) : <variable> is incremented in the cycle that follows the cycle in which the last instruction of <instruction set> is
executed. Then, <variable> is checked to determine whether to exit the loop (in other words, the next statement
is executed). When repeating the loop, processing returns to the first instruction of <instruction set> in this cycle.
(5) : This step is executed in the next cycle.
(6) to (10) : These steps are repeated in the same way as the preceding loop execution.
(11) :
Processing proceeds to the following step (line).
- Sample program
Label Mnemonic parameter1 parameter2 parameter3 parameter4 parameter5
Sequence of execution
㩷
for U(00) 0 3 1
㩷
䋺
(1)
㩷 㩷 㩷
㩷
Y(00)= 1
㩷 㩷 㩷 㩷 䋺
(2)
(5) (8)
㩷
Y(00)= 0
㩷 㩷 㩷 㩷
䋺
(3) (6) (9)
㩷
next
㩷 㩷 㩷 㩷 㩷 䋺
(4)
(7) (10)
㩷
Y(00)= 1
㩷 㩷 㩷 㩷
䋺
(11)
while loop statement Instruction to conditionally execute a pre-conditioned loop
- Format
Format Description
while <condition>
<instruction set>
wend
This instruction executes <instruction set> while <condition> is met.
Note that <condition> is checked before the execution of <instruction
set> .
- Explanation
This instruction executes <instruction set> repeatedly as long as <condition> is met. Note that <condition> is checked
before the execution of <instruction set> . If <condition> is not met, processing proceeds to the wend statement without
executing <instruction set> .
Is <condition> met?
Execute <instruction set>
No
Yes
- Sample program (Condition “X (00) = 0” is met after the loop is executed twice.)
Label Mnemonic parameter1 parameter2 parameter3 parameter4 parameter5
Sequence of execution
㩷
while X(00) = 1
㩷 㩷 䋺
(1)
㩷 㩷 㩷
(5) (9)
㩷
Y(00)= 1
㩷 㩷 㩷 㩷
䋺
(2)
(6)
㩷
Y(00)= 0
㩷 㩷 㩷 㩷
䋺
(3) (7)
㩷
wend
㩷 㩷 㩷 㩷 㩷
䋺
(4)
(8)
㩷
Y(00)= 1
㩷 㩷 㩷 㩷
䋺
(10)
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