ATtiny87 Atmel Corporation, ATtiny87 Datasheet - Page 35
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ATtiny87
Manufacturer Part Number
ATtiny87
Description
Manufacturer
Atmel Corporation
Specifications of ATtiny87
Flash (kbytes)
8 Kbytes
Pin Count
20
Max. Operating Frequency
16 MHz
Cpu
8-bit AVR
Hardware Qtouch Acquisition
No
Max I/o Pins
16
Ext Interrupts
16
Usb Speed
No
Usb Interface
No
Spi
2
Twi (i2c)
1
Uart
1
Lin
1
Graphic Lcd
No
Video Decoder
No
Camera Interface
No
Adc Channels
11
Adc Resolution (bits)
10
Adc Speed (ksps)
15
Analog Comparators
1
Resistive Touch Screen
No
Temp. Sensor
Yes
Crypto Engine
No
Sram (kbytes)
0.5
Eeprom (bytes)
512
Self Program Memory
YES
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
3
Input Capture Channels
1
Pwm Channels
9
32khz Rtc
Yes
Calibrated Rc Oscillator
Yes
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Company
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Manufacturer
Quantity
Price
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8265B–AVR–09/10
In the first domain, the user (code) can easily check the validity of the clock(s)
Command” on page
In the second domain, the lack of a clock results in the code not running. Thus, the presence
of the system clock needs to be monitored by hardware.
Using the on-chip watchdog allows this monitoring. Normally, the watchdog reloading is per-
formed only if the code reaches some specific software labels, reaching these labels proves
that the system clock is running. Otherwise the watchdog reset is enabled. This behavior can
be considered as a clock monitoring.
If the standard watchdog functionality is not desired, the ATtiny87/167 watchdog permits the
system clock to be monitored without having to resort to the complexity of a full software
watchdog handler. The solution proposed in the ATtiny87/167 is to automate the watchdog
reloading with only one command, at the beginning of the session.
So, to monitor the system clock, the user will have two options:
The two options are exclusive.
Note:
Figure 4-6.
The ‘Enable Watchdog in Automatic Reload Mode’ command has priority over the standard
watchdog enabling. In this mode, only the reset function of the watchdog is enabled (no more
watchdog interrupt). The WDP[3:0] bits of the WDTCSR register always determine the watch-
dog timer prescaling.
As the watchdog will not be active before executing the ‘Enable Watchdog in Automatic
Reload Mode’ command, it is recommended to activate this command before switching to an
external clock source (See note on
Notes:
1. Using the standard watchdog features (software reload),
2. Or using the automatic reloading (hardware reload).
Warning:
These two options make sense ONLY if the clock source at RESET is an INTERNAL SOURCE.
The fuse settings determine this operation.
1. ONLY the reset (watchdog reset included) disables this function. The Watchdog System
2. ONLY clock frequencies greater than or equal to (4 * WatchDog Clock Frequency) can be
Reset Flag (WDRF bit of MCUSR register) can be used to monitor the reset cause.
monitored.
WDTCSR
Watchdog Timer with Automatic Reloading.
Interrupt
Register:
Reset
WD
WD
33.).
Internal Bus
WatchDog
page
35).
Reload
0
1
Checker
WatchDog Clock
Enable
Automatic
Reloading
Mode
System CLK
(See “COUT
35