at90ls8535-8mi ATMEL Corporation, at90ls8535-8mi Datasheet - Page 49

• Manufacturer Part Number: at90ls8535-8mi
• Description: 8-bit Microcontroller With 8k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

Watchdog Timer
Watchdog Timer Control
Register – WDTCR
1041H–11/01
The Watchdog Timer is clocked from a separate On-chip oscillator. By controlling the
Watchdog Timer prescaler, the Watchdog reset interval can be adjusted as shown in
Table 21. See characterization data for typical values at other V
(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 AT90S8535 resets and executes from the reset vector. For
timing details on the Watchdog reset, refer to page 22.
To prevent unintentional disabling of the Watchdog, a special turn-off sequence must be
followed when the Watchdog is disabled. Refer to the description of the Watchdog Timer
Control Register for details.
Figure 36. Watchdog Timer
• Bits 7..5 – Res: Reserved Bits
These bits are reserved bits in the AT90S8535 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:
Bit
$21 ($41)
Read/Write
Initial Value
R
Oscillator
7
–
0
350 kHz at V
1 MHz at V
R
6
–
0
CC
CC
= 5V
= 3V
R
5
–
0
WDTOE
R/W
4
0
WDE
R/W
3
0
WDP2
R/W
2
0
AT90S/LS8535
WDP1
R/W
1
0
CC
levels. The WDR
WDP0
R/W
0
0
WDTCR
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