Watchdog timer, The watchdog timer control register - wdtcr, Atmega163(l) – Rainbow Electronics ATmega163L User Manual
Page 51
ATmega163(L)
51
Watchdog Timer
The Watchdog Timer is clocked from a separate on-chip oscillator which runs at 1 Mhz. This is the typical value at V
CC
=
5V. See characterization data for typical values at other V
CC
levels. By controlling the Watchdog Timer prescaler, the
Watchdog reset interval can be adjusted as shown in Table 23 on page 52. The WDR - Watchdog Reset - instruction resets
the Watchdog Timer. Eight different clock cycle periods can be selected to determine the reset period. If the reset period
expires without another Watchdog reset, the ATmega163 resets and executes from the reset vector. For timing details on
the Watchdog reset, refer to page 25.
To prevent unintentional disabling of the watchdog, a special turn-off sequence must be followed when the watchdog is dis-
abled. Refer to the description of the Watchdog Timer Control Register for details.
Figure 40. Watchdog Timer
The Watchdog Timer Control Register - WDTCR
•
Bits 7..5 - Res: Reserved Bits
These bits are reserved bits in the ATmega163 and will always read as zero.
•
Bit 4 - WDTOE: Watchdog Turn-off Enable
This bit must be set (one) when the WDE bit is cleared. Otherwise, the watchdog will not be disabled. Once set, hardware
will clear this bit to zero after four clock cycles. Refer to the description of the WDE bit for a watchdog disable procedure.
•
Bit 3 - WDE: Watchdog Enable
When the WDE is set (one) the Watchdog Timer is enabled, and if the WDE is cleared (zero) the Watchdog Timer function
is disabled. WDE can only be cleared if the WDTOE bit is set(one). To disable an enabled watchdog timer, the following
procedure must be followed:
1.
In the same operation, write a logical one to WDTOE and WDE. A logical one must be written to WDE even though
it is set to one before the disable operation starts.
2.
Within the next four clock cycles, write a logical 0 to WDE. This disables the watchdog.
Bit
7
6
5
4
3
2
1
0
$21 ($41)
-
-
-
WDTOE
WDE
WDP2
WDP1
WDP0
WDTCR
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial value
0
0
0
0
0
0
0
0
1 MHz at V
CC
= 5V
OSCILLATOR