ATmega32U4 Atmel Corporation, ATmega32U4 Datasheet - Page 37

• Manufacturer Part Number: ATmega32U4
• Manufacturer: Atmel Corporation

Specifications of ATmega32U4

• Flash (kbytes): 32 Kbytes
• Pin Count: 44
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 14
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 26
• Ext Interrupts: 13
• Usb Transceiver: 1
• Usb Speed: Full Speed
• Usb Interface: Device
• Spi: 2
• Twi (i2c): 1
• Uart: 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): 3.3
• Eeprom (bytes): 1024
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 4
• Output Compare Channels: 12
• Input Capture Channels: 2
• Pwm Channels: 8
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

6.8.5
6.9
6.9.1
7766F–AVR–11/10
Clock Output Buffer
CLKSTA – Clock Status Register
System Clock Prescaler
• Bit 7-4 – RCCKSEL[3:0]: CKSEL for RC oscillator
Clock configuration for the RC Oscillator. After a reset, this part of the register is loaded with the
0010b value that corresponds to the RC oscillator. Modifying this value by firmware before
switching to RC oscillator is prohibited because the RC clock will not start.
• Bit 3-0 – EXCKSEL[3:0]: CKSEL for External Clock / Low Power Crystal Oscillator
Clock configuration for the External Clock / Low Power Crystal Oscillator. After a reset, if the
External Clock / Low Power Crystal Oscillator is selected by fuse bits, this part of the register is
loaded with the fuse configuration. Firmware can modify it to change the start-up time after the
clock switch.
See
Power Crystal Oscillator, Calibrated Internal RC Oscillator, and External Clock modes are
allowed.
• Bit 7-2 - Reserved bits
These bits are reserved and will always read as zero.
• Bit 1 – RCON: RC Oscillator On
This bit is set by hardware to one if the RC Oscillator is running.
This bit is set by hardware to zero if the RC Oscillator is stopped.
• Bit 0 – EXTON: External Clock / Low Power Crystal Oscillator On
This bit is set by hardware to one if the External Clock / Low Power Crystal Oscillator is running.
This bit is set by hardware to zero if the External Clock / Low Power Crystal Oscillator is
stopped.
The device can output the system clock on the CLKO pin. To enable the output, the CKOUT
Fuse has to be programmed. This mode is suitable when the chip clock is used to drive other cir-
cuits on the system. The clock also will be output during reset, and the normal operation of I/O
pin will be overridden when the fuse is programmed. Any clock source, including the internal RC
Oscillator, can be selected when the clock is output on CLKO. If the System Clock Prescaler is
used, it is the divided system clock that is output.
The AVR USB has a system clock prescaler, and the system clock can be divided by setting the
“CLKPR – Clock Prescaler Register” on page
tem clock frequency and the power consumption when the requirement for processing power is
low. This can be used with all clock source options, and it will affect the clock frequency of the
CPU and all synchronous peripherals. clk
as shown in
When switching between prescaler settings, the System Clock Prescaler ensures that no
glitches occurs in the clock system. It also ensures that no intermediate frequency is higher than
neither the clock frequency corresponding to the previous setting, nor the clock frequency corre-
sponding to the new setting.
Bit
Read/Write
Initial Value
“Device Clocking Options Select(1)” on page 28
Table
7
-
R
0
6-10.
6
-
R
0
5
-
R
0
4
-
R
0
I/O
, clk
38. This feature can be used to decrease the sys-
3
-
R
0
ADC
, clk
for EXCKSEL[3:0] configuration. Only Low
2
-
R
CPU
, and clk
1
RCON
R
ATmega16/32U4
FLASH
0
EXTON
R
are divided by a factor
CLKSTA
37