ATmega128A Atmel Corporation, ATmega128A Datasheet - Page 38

• Manufacturer Part Number: ATmega128A
• Manufacturer: Atmel Corporation

Specifications of ATmega128A

• Flash (kbytes): 128 Kbytes
• Pin Count: 64
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 53
• Ext Interrupts: 8
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• Uart: 2
• 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: No
• Crypto Engine: No
• Sram (kbytes): 4
• Eeprom (bytes): 4096
• 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: 8
• Input Capture Channels: 2
• Pwm Channels: 7
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

8.1.3
8.1.4
8.1.5
8.1.6
8151H–AVR–02/11
Flash Clock – clk
Asynchronous Timer Clock – clk
ADC Clock – clk
XDIV - XTAL Divide Control Register
The Flash clock controls operatio
n of the Flash interface. The Flash clock is usually active simultaneously with the CPU clock.
The Asynchronous Timer clock allows the Asynchronous Timer/Counter to be clocked directly
from an external 32kHz clock crystal. The dedicated clock domain allows using this Timer/Coun-
ter as a real-time counter even when the device is in sleep mode.
The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks
in order to reduce noise generated by digital circuitry. This gives more accurate ADC conversion
results.
The XTAL Divide Control Register is used to divide the Source clock frequency by a number in
the range 2 - 129. This feature can be used to decrease power consumption when the require-
ment for processing power is low.
• Bit 7 – XDIVEN: XTAL Divide Enable
When the XDIVEN bit is written one, the clock frequency of the CPU and all peripherals (clk
clk
can be written run-time to vary the clock frequency as suitable to the application.
• Bits 6:0 – XDIV6:XDIV0: XTAL Divide Select Bits 6 - 0
These bits define the division factor that applies when the XDIVEN bit is set (one). If the value of
these bits is denoted d, the following formula defines the resulting CPU and peripherals clock
frequency f
The value of these bits can only be changed when XDIVEN is zero. When XDIVEN is written to
one, the value written simultaneously into XDIV6:XDIV0 is taken as the division factor. When
XDIVEN is written to zero, the value written simultaneously into XDIV6:XDIV0 is rejected. As the
divider divides the master clock input to the MCU, the speed of all peripherals is reduced when a
division factor is used.
When the system clock is divided, Timer/Counter0 can be used with Asynchronous clock only.
The frequency of the asynchronous clock must be lower than 1/4th of the frequency of the
scaled down Source clock. Otherwise, interrupts may be lost, and accessing the Timer/Counter0
registers may fail.
Bit
Read/Write
Initial Value
ADC
FLASH
ADC
, clk
CPU
CLK
, clk
:
XDIVEN
R/W
FLASH
7
0
ASY
) is divided by the factor defined by the setting of XDIV6 - XDIV0. This bit
XDIV6
R/W
6
0
XDIV5
R/W
5
0
f
CLK
=
XDIV4
R/W
4
0
Source clock
--------------------------------- -
129 d
XDIV3
–
R/W
3
0
XDIV2
R/W
2
0
XDIV1
ATmega128A
R/W
1
0
XDIV0
R/W
0
0
XDIV
I/O
38
,