Figure 10-6 Watchdog Timer - Toshiba TX79 Series User Manual

10.5.3 Watchdog Timer Mode Operation
This mode is set up by setting the timer mode (TMODE) field of the Timer Control Register
(TMTCR) to 0b10 (binary). In this mode, when the Timer/Counter Enable (TCE) bit of the
TMTCR register is set to "1", the 24-bit counter begins counting. When the count value
reaches the value in register TMCPRA, the comparator sets the Watchdog Timer Interrupt
Status bit (TWIS) of the Timer Interrupt Status Register (TMTISR) to "1". This also causes
the interrupt control logic to assert the Watchdog Timer Interrupt Request signal
WDTINTREQ*, if the Watchdog Timer Interrupt Enable bit (TWIE) in the Watchdog Timer
Mode Register (TMWTMR) is set to "1". If the TWIE bit is "0", WDTINTREQ* is masked, and
is thus not asserted. Writing a "1" to the TWIS bit is ignored.
To clear the 24-bit counter, the Watchdog Timer Clear (TWC) bit of the Watchdog Timer
Mode Register (TMWTMR) is set to "1". The TWC bit is automatically reset to "0" after the
24-bit counter is cleared.
When the Timer/Counter Enable bit (TCE) is cleared and the Watchdog Timer Disable
(WDIS) bit of the TMWTMR register is set to "1", the Watchdog Timer Counter is disabled.
However, when the WDIS bit is "0", count operation cannot be stopped by clearing the TCE
bit to "0". In addition, the TWIE bit cannot be cleared while the WDIS bit is "0". Another way
to disable the watchdog timer (by masking the interrupt) is to clear the Watchdog Timer
Enable bit (TWIE) while WDIS bit is set to "1". The WDIS bit is automatically cleared when
the Watchdog Timer becomes disabled by one of the methods described above.
The count value for the Watchdog Timer can be read from the TMTRR register.
Count Value
0x000000
TMODE10
TCE
TWC
TWIE
WDIS
CRE
TWIS
WDTINTREQ*
Figure 10-6 Watchdog Timer Mode Operation of Timer/Counter
TX7901 User's Manual (Rev. 6.30T – Nov, 2001)
Chapter 10: Programmable Timer/Contents
TMCPRA Compare Value
1 1
0
1 1
1
1
0
0
10-20
10
1
1
1
0
1
1
0
Reset State
Time
1
1
Reset State