Toshiba TLCS-900/L1 Series Manual page 194

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
3.12.1 Configuration
Figure 3.12.1 is a block diagram of he watchdog timer (WDT).
WDMOD
<WDTP1:0>
f
SYS
(f /2)
FPH
Internal reset
Note: It needs to care designing the total machine set, because watchdog timer can't
operate completely by external noise.
pin is not changed)
RESET
Selector
21
15 17 19
2 2 2 2
Binary counter
(22 stages)
Reset
Write
4EH
WDT control register WDCR
Internal data bus
Figure 3.12.1 Block Diagram of Watchdog Timer
91C824-192
WDMOD<RESCR>
Reset control
WDTI interrupt
Q
R S
Write WDMOD<WDTE>
B1H
TMP91C824
RESET
Internal reset
2008-02-20