ATtiny40 Atmel Corporation, ATtiny40 Datasheet - Page 24

• Manufacturer Part Number: ATtiny40
• Manufacturer: Atmel Corporation

Specifications of ATtiny40

• Flash (kbytes): 4 Kbytes
• Pin Count: 20
• Max. Operating Frequency: 12 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 12
• Hardware Qtouch Acquisition: Yes
• Max I/o Pins: 18
• Ext Interrupts: 18
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 12
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: Yes
• Crypto Engine: No
• Sram (kbytes): 0.25
• 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: 2
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

6.5
6.5.1
6.5.2
24
Register Description
ATtiny40
CLKMSR – Clock Main Settings Register
CLKPSR – Clock Prescale Register
• Bits 7:2 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bits 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 7:4 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bits 3:0 – CLKPS[3:0]: Clock Prescaler Select Bits 3 - 0
These bits define the division factor between the selected clock source and the internal system
clock. These bits can be written at run-time to vary the clock frequency and suit the application
Bit
0x37
Read/Write
Initial Value
Bit
0x36
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
Selection of Main Clock
R
R
7
–
0
7
–
0
CLKM0
0
1
0
1
R
R
6
–
0
6
–
0
R
R
5
–
0
5
–
0
Main Clock Source
Calibrated Internal 8 MHzOscillator
Internal 128 kHz Oscillator (WDT Oscillator)
External clock
Reserved
R
R
0
0
4
–
4
–
Table
CLKPS3
6-3.
R/W
3
–
R
0
3
0
CLKPS2
R
2
–
0
R/W
2
0
CLKMS1
CLKPS1
R/W
1
0
R/W
1
1
CLKMS0
R/W
CLKPS0
0
0
R/W
0
1
CLKMSR
8263A–AVR–08/10
CLKPSR