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Flowchart of CPU Operation
YES
NO
NO
Power application
Clears IR area and
resets all timers
Checks I/O Unit connections
Resets watchdog timer
Checks hardware and
Program Memory
Check OK?
Services Host Link
ALARM/ERROR
Sets error flags and turns
ON or flashes indicator
Executes user program
Resets watchdog timer
Refreshes input bits
and output signals
ALARM
(Flashing)
ERROR
(Solid ON)
Services Peripheral Devices
Resets watchdog timer and
program address counter
End of program?
YES
Minimum
cycle time?
NO
YES
Resets watchdog timer and waits
until the set cycle time has elapsed
Calculates cycle time
Services SYSMAC LINK and
SYSMAC NET Link Units
Initialization
on power-up
Overseeing
processes
Program
execution
Cycle time
calculation
I/O
refreshing
Host Link Unit
servicing
Peripheral
device
servicing
SYSMAC LINK
and SYSMAC
NET Link Unit
servicing
PC
cycle
time
Services RS-232C
port
RS-232C port
servicing
Note A minimum cycle
time can be set
either in DM 6619
of the PC Setup
or by executing
SCAN(18).
Cycle Time Section 6-1