TMP91C824
91C824-192
2008-02-20
3.12 Watchdog Timer (Runaway detection timer)
The TMP91C824 features a watchdog timer for detecting runaway.
The watchdog timer (WDT) is used to return the CPU to normal state when it detects that
the CPU has started to malfunction (Runaway) due to causes such as noise.
When the watchdog timer detects a malfunction, it generates a non-maskable interrupt
INTWD to notify the CPU. Connecting the watchdog timer output to the reset pin internally
forces a reset. (The level of external
RESET
pin is not changed)
3.12.1 Configuration
Figure 3.12.1 is a block diagram of he watchdog timer (WDT).
Figure 3.12.1 Block Diagram of Watchdog Timer
Note: It needs to care designing the total machine set, because watchdog timer can’t
operate completely by external noise.
Internal reset
WDMOD
<WDTP1:0>
WDMOD<WDTE>
Reset
WDT control register WDCR
Q
R S
2
21
Internal reset
WDMOD<RESCR>
WDTI interrupt
f
SYS
(f
FPH
/2)
Selector
2
19
2
17
2
15
Internal data bus
Write
B1H
Write
4EH
RESET
Reset control
Binary counter
(22 stages)