Rainbow Electronics ATmega8515L - Manual (Page 48)

48
ATmega8515(L)
2512A–AVR–04/02
Figure 27. Watchdog Timer
Watchdog Timer Control
Register – WDTCR
• Bits 7..5 – Res: Reserved Bits
These bits are reserved bits in the ATmega8515 and will always read as zero.
• Bit 4 – WDCE: Watchdog Change Enable
This bit must be set when the WDE bit is written to logic zero. Otherwise, the Watchdog
will not be disabled. Once written to one, hardware will clear this bit after four clock
cycles. Refer to the description of the WDE bit for a Watchdog disable procedure. In
Safety Levels 1 and 2, this bit must also be set when changing the prescaler bits. See
“Timed Sequences for Changing the Configuration of the Watchdog Timer” on page 50.
• Bit 3 – WDE: Watchdog Enable
When the WDE is written to logic one, the Watchdog Timer is enabled, and if the WDE is
written to logic zero, the Watchdog Timer function is disabled. WDE can only be cleared
if the WDCE bit has logic level one. To disable an enabled Watchdog Timer, the follow-
ing procedure must be followed:
Table 20. WDT Configuration as a Function of the Fuse Settings of S8515C and
WDTON.
S8515C WDTON
Safety
Level
WDT
Initial
State
How to Disable
the WDT
How to
Change Time-
out
Unprogrammed Unprogrammed 1 Disabled Timed sequence Timed
sequence
Unprogrammed Programmed 2 Enabled Always enabled Timed
sequence
Programmed Unprogrammed 0 Disabled Timed sequence No restriction
Programmed Programmed 2 Enabled Always enabled Timed
sequence
WATCHDOG
OSCILLATOR
Bit 7 6 5 4 3 2 1 0
– – – WDCE 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