ATmega64A Atmel Corporation, ATmega64A Datasheet - Page 143

• Manufacturer Part Number: ATmega64A
• Manufacturer: Atmel Corporation

Specifications of ATmega64A

• Flash (kbytes): 64 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): 2048
• 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

16. Timer/Counter3, Timer/Counter2 and Timer/Counter1 Prescalers
16.0.1
16.0.2
16.0.3
8160C–AVR–07/09
Internal Clock Source
Prescaler Reset
External Clock Source
Timer/Counter3, Timer/Counter2 and Timer/Counter1 share the same prescaler module, but the
Timer/Counters can have different prescaler settings. The description below applies to all of the
mentioned Timer/Counters.
The Timer/Counter can be clocked directly by the system clock (by setting the CSn2:0 = 1). This
provides the fastest operation, with a maximum Timer/Counter clock frequency equal to system
clock frequency (f
clock source. The prescaled clock has a frequency of either f
f
The prescaler is free running, for example, it operates independently of the Clock Select logic of
the Timer/Counter, and it is shared by Timer/Counter1, Timer/Counter2, and Timer/Counter3.
Since the prescaler is not affected by the Timer/Counter’s clock select, the state of the prescaler
will have implications for situations where a prescaled clock is used. One example of prescaling
artifacts occurs when the timer is enabled and clocked by the prescaler (6 > CSn2:0 > 1). The
number of system clock cycles from when the timer is enabled to the first count occurs can be
from 1 to N+1 system clock cycles, where N equals the prescaler divisor (8, 64, 256, or 1024).
It is possible to use the Prescaler Reset for synchronizing the Timer/Counter to program execu-
tion. However, care must be taken if the other Timer/Counter that shares the same prescaler
also use prescaling. A Prescaler Reset will affect the prescaler period for all Timer/Counters it is
connected to.
An external clock source applied to the Tn pin can be used as Timer/Counter clock
(clk
tion logic. The synchronized (sampled) signal is then passed through the edge detector.
16-1
logic. The registers are clocked at the positive edge of the internal system clock (
is transparent in the high period of the internal system clock.
The edge detector generates one clk
tive (CSn2:0 = 6) edge it detects.
Figure 16-1. Tn Pin Sampling
CLK_I/O
T1
shows a functional equivalent block diagram of the Tn synchronization and edge detector
/clk
/1024.
clk
Tn
T2
I/O
/clk
T3
). The Tn pin is sampled once every system clock cycle by the pin synchroniza-
D Q
LE
CLK_I/O
). Alternatively, one of four taps from the prescaler can be used as a
D Q
T1
/clk
T
2
/clk
T
3
pulse for each positive (CSn2:0 = 7) or nega-
D
CLK_I/O
Q
Edge Detector
/8, f
CLK_I/O
ATmega64A
/64, f
clk
Tn_sync
(To Clock
Select Logic)
CLK_I/O
I/O
). The latch
/256, or
Figure
143