6

4756D–AUTO–11/05

U5021M

Figure 4-4.

Pulse Diagram of a Correct Trigger Sequence During the Short Watchdog Time

Figure 4-5 shows the switch-over from the short to the long watchdog mode. The wake-up signal

during the enable time, t

The watchdog can be switched back from the long to the short watchdog mode with a low poten-

tial at the mode pin (pin 3).

Figure 4-5.

Pulse Diagram of the Long Watchdog Time

5.

State Diagram

The kernel of the watchdog is a finite state machine. Figure 5-1 shows the state diagram with all

possible states and transmissions. Many transmissions are controlled by an internal timer. The

numbers for the time-outs are the same as on the pulse diagrams.

V

DD

Reset out

Mode

Trigger

Enable

t

0

Pin 4

Pin 2

Pin 3

Pin 5

Pin 6

t

1

t

2

t

3

t

2

t

trig

t

2

Wake-up

Enable

Mode

Trigger

Reset out

Pin 4

Pin 2

Pin 3

Pins 1

Pin 5

t

4

t

5

t

6

t

1