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4.A2CCPU
- - - - - - - - - - - - - - - - - - - - MELSEC·A
4.1.7
Scan time
(1)
Scan time
Scan time is the period in which PC one scan [0 to END (FEND)) is
executed.
I
Scan time
o
- - - - - - - - - - o i [
Processing of counters and timers
Self-diagnosis check
T--~T_-
- - - - - - _ - _ - _ _
sequence
program
Fig. 4.6 Scan Time
(2)
Scan time confirmation
The A2CCPU counts the scan time between an END (FEND) instruction
to the next END (FEND) instruction and registers the counted scan time
in special registers D9017 to D9019.
(a) Special register data (D9017 to D9019)
• D9017 : The minimum scan time
• D9018 : Present scan time
• D9019 : The maximum scan time
(b) Accuracy of scan time
The accurate to scan time counted by the programmable controller
is accurate to ± 10 msec.
Therefore, if the data in D9017 to D9019 is 5, actual scan time is in
the range of 40 to 60 msec.
(c) The data in D9017 to D9019 is not cleared when the WDT instruction
is executed; the scan time between an END (FEND) instruction and
the next END (FEND) instruction is registered.
IREMARKsl
(1) The scan time can be confirmed
by the circuit monitoring operation using a peripheral
device.
*
Scan time of 0 to 20 msec
: 10 msec is displayed
'*
Scan time of 10 to 30 msec: 20 msec is displayed
(2) The constant scan function allows the scan time of every scan to be fixed to
8
constant
value. For more details on the constant scan function, see Section 4.2.1.
4-10

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