ATtiny4 Atmel Corporation, ATtiny4 Datasheet - Page 21

• Manufacturer Part Number: ATtiny4
• Manufacturer: Atmel Corporation

Specifications of ATtiny4

• Flash (kbytes): 0.5 Kbytes
• Pin Count: 6
• Max. Operating Frequency: 12 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 1
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 4
• Ext Interrupts: 4
• Usb Speed: No
• Usb Interface: No
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 0.03
• Self Program Memory: NO
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 125
• I/o Supply Class: 1.8 to 5.5
• Operating Voltage (vcc): 1.8 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 1
• Output Compare Channels: 2
• Input Capture Channels: 1
• Pwm Channels: 2
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

6.5
6.5.1
6.5.2
8127E–AVR–11/11
Register Description
CLKMSR – Clock Main Settings Register
OSCCAL – Oscillator Calibration Register
• Bit 7:2 – Res: Reserved Bits
These bits are reserved and always read zero.
• Bit 1:0 – CLKMS[1:0]: Clock Main Select Bits
These bits select the main clock source of the system. The bits can be written at run-time to
switch the source of the main clock. The clock system ensures glitch free switching of the main
clock source.
The main clock alternatives are shown in
Table 6-3.
To avoid unintentional switching of main clock source, a protected change sequence must be
followed to change the CLKMS bits, as follows:
.
• Bits 7:0
The oscillator calibration register is used to trim the calibrated internal oscillator and remove pro-
cess variations from the oscillator frequency. A pre-programmed calibration value is
automatically written to this register during chip reset, giving the factory calibrated frequency as
specified in
The application software can write this register to change the oscillator frequency. The oscillator
can be calibrated to frequencies as specified in
Oscillator,” on page
The CAL[7:0] bits are used to tune the frequency of the oscillator. A setting of 0x00 gives the
lowest frequency, and a setting of 0xFF gives the highest frequency.
Bit
0x37
Read/Write
Initial Value
Bit
0x39
Read/Write
Initial Value
1. Write the signature for change enable of protected I/O register to register CCP
2. Within four instruction cycles, write the CLKMS bits with the desired value
CLKM1
0
0
1
1
–
Table 16-2, “Calibration Accuracy of Internal RC Oscillator,” on page
CAL[7:0]: Oscillator Calibration Value
CAL7
Selection of Main Clock
R/W
R
X
7
–
0
7
119. Calibration outside the range given is not guaranteed.
CLKM0
CAL6
R/W
R
0
1
0
1
X
6
–
0
6
CAL5
R/W
R
5
–
0
5
X
Main Clock Source
Calibrated Internal 8 MHzOscillator
Internal 128 kHz Oscillator (WDT Oscillator)
External clock
Reserved
CAL4
R/W
4
–
R
0
4
X
Table
CAL3
R/W
Table 16-2, “Calibration Accuracy of Internal RC
6-3.
R
X
3
–
0
3
CAL2
R/W
R
X
2
–
0
2
CLKMS1
CAL1
R/W
R/W
X
1
1
0
ATtiny4/5/9/10
CLKMS0
CAL0
R/W
X
R/W
0
0
0
OSCCAL
CLKMSR
119.
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