
TIMERS and TIMER/COUNTERS
S3C7559/P7559
11-8
WATCHDOG TIMER MODE REGISTER (WDMOD)
The watchdog timer mode register, WDMOD, is a 8-bit write-only register. WDMOD register controls to enable or
disable the watchdog function. WDMOD values are set to logic “A5H” following RESET and this value enables the
watchdog timer. Watchdog timer is set to the longest interval because BT overflow signal is generated with the
longest interval.
WDMOD
Watchdog Timer Enable/Disable Control
5AH
Disable watchdog timer function
Any other value
Enable watchdog timer function
WATCHDOG TIMER COUNTER (WDCNT)
The watchdog timer counter, WDCNT, is a 3-bit counter. WDCNT is automatically cleared to logic zero, and
restarts whenever the WDTCF register control bit is set to “1”. RESET, stop, and wait signal clears the WDCNT to
logic zero also.
WDCNT increments each time a clock pulse of the overflow frequency determined by the current BMOD bit
setting is generated. When WDCNT has incremented to hexadecimal ‘07H’, it is cleared to ‘00H’ and an overflow
is generated. The overflow causes the system RESET. When the interrupt request is generated, BCNT
immediately resumes counting incoming clock signals.
WATCHDOG TIMER COUNTER CLEAR FLAG (WDTCF)
The watchdog timer counter clear flag, WDTCF, is a 1-bit write instruction. When WDTCF is set to one, it clears
the WDCNT to zero and restarts the WDCNT. WDTCF register bits 2–0 are always logic zero.
Table 11-3. Watchdog Timer Interval Time
BMOD
BT Input Clock
WDCNT Input Clock
WDT Interval Time
x000b
fxx/212
fxx/(212
× 28)
(7–8)
× (212 × 28) / fxx = 1.75–2 sec
x011b
fxx/29
fxx/(29
× 28)
(7–8)
× (29 × 28) / fxx = 218.7–250 ms
x101b
fxx/27
fxx/(27
× 28)
(7–8)
× (27 × 28) / fxx = 54.6–62.5 ms
x111b
fxx/25
fxx/(25
× 28)
(7–8)
× (25 × 28) / fxx = 13.6–15.6 ms
NOTES:
1.
Clock frequencies assume a system oscillator clock frequency (fx) of 4.19 MHz
2.
fxx = system clock frequency.
3.
When the watchdog timer is enabled or the 3-bit counter of the watchdog timer is cleared to “0”, the BCNT value is not
cleared but increased continuously. As a result, the 3-bit counter of the watchdog timer (WDCNT) can be increased
by 1. For example, when the BMOD value is x000b and the watchdog timer is enabled, the watchdog timer interval time
is from 23
× 212 × 28/fxx to (23–1) × 212 × 28/fxx.