ATtiny20 Atmel Corporation, ATtiny20 Datasheet - Page 34

• Manufacturer Part Number: ATtiny20
• Manufacturer: Atmel Corporation

Specifications of ATtiny20

• Flash (kbytes): 2 Kbytes
• Pin Count: 14
• Max. Operating Frequency: 12 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 5
• Hardware Qtouch Acquisition: Yes
• Max I/o Pins: 12
• Ext Interrupts: 12
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: Yes
• Crypto Engine: No
• Sram (kbytes): 0.12
• Self Program Memory: NO
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 1.8 to 5.5
• Operating Voltage (vcc): 1.8 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 2
• Output Compare Channels: 4
• Input Capture Channels: 1
• Pwm Channels: 3
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

8.4.1
8.4.1.1
8.4.1.2
34
ATtiny20
Procedure for Changing the Watchdog Timer Configuration
Safety Level 1
Safety Level 2
Figure 8-7.
The Wathdog Timer can also be configured to generate an interrupt instead of a reset. This can
be very helpful when using the Watchdog to wake-up from Power-down.
To prevent unintentional disabling of the Watchdog or unintentional change of time-out period,
two different safety levels are selected by the fuse WDTON as shown in
See
Table 8-1.
The sequence for changing configuration differs between the two safety levels, as follows:
In this mode, the Watchdog Timer is initially disabled, but can be enabled by writing the WDE bit
to one without any restriction. A special sequence is needed when disabling an enabled Watch-
dog Timer. To disable an enabled Watchdog Timer, the following procedure must be followed:
In this mode, the Watchdog Timer is always enabled, and the WDE bit will always read as one. A
protected change is needed when changing the Watchdog Time-out period. To change the
Watchdog Time-out, the following procedure must be followed:
WDTON
Unprogrammed
Programmed
1. Write the signature for change enable of protected I/O registers to register CCP
2. Within four instruction cycles, in the same operation, write WDE and WDP bits
1. Write the signature for change enable of protected I/O registers to register CCP
2. Within four instruction cycles, write the WDP bit. The value written to WDE is irrelevant
“Procedure for Changing the Watchdog Timer Configuration” on page 34
Watchdog Timer
WDT Configuration as a Function of the Fuse Settings of WDTON
Safety
Level
1
2
WATCHDOG
OSCILLATOR
RESET
128 kHz
WDP0
WDP1
WDP2
WDP3
WDE
WDT
Initial State
Disabled
Enabled
How to
Disable the WDT
Protected change
sequence
Always enabled
MCU RESET
PRESCALER
WATCHDOG
MUX
How to
Change Time-out
No limitations
Protected change
sequence
Table 8-1 on page
for details.
8235B–AVR–04/11
34.