AT90S2313-4PI View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
'AT90S2313-4PI' PDF : 92 Pages View PDF
Watchdog Timer
AT90S2313
The Watchdog Timer is clocked from a separate On-chip Oscillator that runs at 1 MHz.
This is the typical value at VCC = 5V. See characterization data for typical values at other
VCC levels. By controlling the Watchdog Timer prescaler, the Watchdog Reset interval
can be adjusted. See Table 14 for a detailed description. 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 AT90S2313 resets and executes from the Reset Vector. For tim-
ing details on the Watchdog Reset, refer to page 21.
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 33. Watchdog Timer
Watchdog Timer Control
Register – WDTCR
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
• Bits 7..5 – Res: Reserved Bits
These bits are reserved bits in the AT90S2313 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 proce-
dure must be followed:
37
0839I–AVR–06/02
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