P80C562 Philips Semiconductors, P80C562 Datasheet - Page 23

• Manufacturer Part Number: P80C562
• Description: 8-bit microcontroller
• Manufacturer: Philips Semiconductors

Philips Semiconductors
12.3
In addition to Timer T2 and the standard timers, a
Watchdog Timer is also available, consisting of an 11-bit
prescaler and a 8-bit timer. The functional diagram of the
Watchdog Timer is shown in Fig.11. The timer is
incremented every t seconds,
where:
When a timer overflow occurs, the microcontroller is reset
and a reset output pulse is generated at the RST pin.
To prevent a system reset the timer must be reloaded in
time by the application software. If the processor suffers a
hardware/ software malfunction, the software will fail to
reload the timer. This failure will produce a reset upon
overflow thus preventing the processor running out of
control.
1997 Apr 08
handbook, full pagewidth
8-bit microcontroller
Watchdog Timer (T3)
t
f
EW
osc
=
12 2048
------------------------- -
/12
f
OSC
write
T3
PRESCALER
Fig.11 Functional diagram of Watchdog Timer.
11-BIT
CLEAR
TIMER T3 (8-BIT)
PCON.4
INTERNAL BUS
INTERNAL BUS
LOAD
23
CLEAR
The Watchdog Timer can only be reloaded if the condition
flag WLE in the Power Control Register has been
previously set by software. At the moment the counter is
loaded the condition flag is automatically cleared.
The timer interval between the timer's reloading and
occurrence of a reset, is dependent upon the reloaded
value. For example, this may range from 2 ms to 0.5 s
when using an oscillator frequency of 12 MHz. In the Idle
state the Watchdog Timer and reset circuitry remain
active.
The Watchdog Timer is controlled by the Enable
Watchdog pin (EW). A logic 0 enables the Watchdog
Timer and disables the Power-down mode. A logic 1
disables the Watchdog Timer and enables the
Power-down mode.
WLE
LOADEN
internal
reset
overflow
LOADEN
PD
PCON.1
P83C562; P80C562
Product specification
V DD
P
R
RST
MBC753
RST