111
Power application
Initialization on power-up
Overseeing processes
Program execution
I/O refresh
Service Programming
Console commands
Service PC Link
•
Transfer the program from EEPROM to RAM.
•
Resets the watchdog timer.
•
Using the programmed code, executes each
instruction from address 000 through to the
END instruction
•
Output Refresh
Refreshes output bits according to output bit
status (results of the executed program).
•
Services the Programming Console (monitor,
edits, etc.).
•
Data communication with other PCs
via the Link Adapter.
•
Resets data areas (except DR area), resets all
timers, and checks the link status.
•
Checks the RUN status and Program Memory.
•
Input Refresh
Refreshes input bits according to input signals.
PC scan time
The time required to
perform this process.
A
B
C
D
E
•
After power application, there is a 2.5-s delay
before the start of initialization.
The first initialization process is performed only once, immediately after pow-
er is applied to the PC. The remaining operations are performed in cyclic
fashion, with each cycle forming one scan. The scan time is the time that is
required for the CPU to complete one of these cycles. This cycle includes
basically five types of operation.
Overseeing
Program execution
I/O refresh
Programming Console servicing
PC Link servicing
The scan time is the total time required for the PC to perform all of the above
operations. The present and maximum scan time can be read out from the
Programming Console with the SP16 or SP20. Refer to 3-8-2 Reading the
Scan Time for details.
All peripheral devices are serviced once each scan in the order given above.
Within the PC, the watchdog timer measures the scan time and compares it
to a set value. If the scan time exceeds the set value of the watchdog timer,
100 ms, a CPU error is generated and the CPU stops. One scan time is ap-
proximately 300
µ
s plus the time required for program execution.
3-10
I/O Response Time
The I/O response time is the time it takes for the PC to output a control signal
after it has received an input signal. The time it takes to respond depends on
the scan time and when the CPU receives the input signal relative to the I/O
refresh period.
Watchdog Timer and Long
Scan Times
I/O Response Time
Section 3-10