Description
Asem S.p.A. 9
Watch-dog
The watch-dog allows system restart after a crash caused by
hardware or software.
It is based on a timer with a period that can be programmed from
among four pre-defined values. The application software must
constantly refresh the watch-dog with a period that is less than that
of the timer, so as to keep the watch-dog from intervening.
If this refresh does not occur, at the end of the pre-established time:
• the watch-dog LED on the CPU 1021/A will come on
• bit 0 of the port I/O 568h will be set to logic state 1. The
application software will subsequently be able to read it.
• There will then be generated a Reset, based on the settings
made by the user.
Selection of generated signal (JP15)
After intervention of the watch-dog, the LED and the bit 0 of the port
568h can be returned to the initial conditions through a command of
the application software or by pressing the key Reset watch-dog.
States of watch-dog
The watch-dog has four operating states:
1. Idle
(initial inactive state) waiting for command out 565h=80h to
change to Set.
2. Set
waiting for command out 566h=nh (0<n<=FFh), to set the WD
intervention time (from 0 up to 255 seconds) and change to Run.
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