ATmega168P Atmel Corporation, ATmega168P Datasheet - Page 139

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ATmega168P

Manufacturer Part Number
ATmega168P
Description
Manufacturer
Atmel Corporation
Datasheets

Specifications of ATmega168P

Flash (kbytes)
16 Kbytes
Pin Count
32
Max. Operating Frequency
20 MHz
Cpu
8-bit AVR
# Of Touch Channels
16
Hardware Qtouch Acquisition
No
Max I/o Pins
23
Ext Interrupts
24
Usb Speed
No
Usb Interface
No
Spi
2
Twi (i2c)
1
Uart
1
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
Yes
Crypto Engine
No
Sram (kbytes)
1
Eeprom (bytes)
512
Self Program Memory
YES
Dram Memory
No
Nand Interface
No
Picopower
Yes
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
3
Output Compare Channels
6
Input Capture Channels
1
Pwm Channels
6
32khz Rtc
Yes
Calibrated Rc Oscillator
Yes

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17. Timer/Counter0 and Timer/Counter1 Prescalers
17.1
17.2
17.3
8025M–AVR–6/11
Internal Clock Source
Prescaler Reset
External Clock Source
”8-bit Timer/Counter0 with PWM” on page 92
111
tings. The description below applies to both Timer/Counter1 and Timer/Counter0.
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, i.e., operates independently of the Clock Select logic of the
Timer/Counter, and it is shared by Timer/Counter1 and Timer/Counter0. 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 uses prescaling. A prescaler reset will affect the prescaler period for all Timer/Counters it is
connected to.
An external clock source applied to the T1/T0 pin can be used as Timer/Counter clock
(clk
logic. The synchronized (sampled) signal is then passed through the edge detector.
shows a functional equivalent block diagram of the T1/T0 synchronization and edge detector
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
(CSn2:0 = 6) edge it detects.
Figure 17-1. T1/T0 Pin Sampling
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles
from an edge has been applied to the T1/T0 pin to the counter is updated.
CLK_I/O
T1
share the same prescaler module, but the Timer/Counters can have different prescaler set-
/clk
/1024.
Tn
clk
T0
I/O
). The T1/T0 pin is sampled once every system clock cycle by the pin synchronization
CLK_I/O
D
LE
Q
). Alternatively, one of four taps from the prescaler can be used as a
Synchronization
D
Q
T1
/clk
T
0
pulse for each positive (CSn2:0 = 7) or negative
and
”16-bit Timer/Counter1 with PWM” on page
ATmega48P/88P/168P
D
CLK_I/O
Q
/8, f
CLK_I/O
Edge Detector
/64, f
clk
CLK_I/O
I/O
Tn_sync
(To Clock
Select Logic)
Figure 17-1
). The latch
/256, or
139

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