ATMEGA2561-16AI Atmel, ATMEGA2561-16AI Datasheet - Page 169
![IC AVR MCU 256K 16MHZ 64TQFP](/photos/12/13/121332/313-64-tqfp_sml.jpg)
ATMEGA2561-16AI
Manufacturer Part Number
ATMEGA2561-16AI
Description
IC AVR MCU 256K 16MHZ 64TQFP
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA2561-16AI
Core Processor
AVR
Core Size
8-Bit
Speed
16MHz
Connectivity
EBI/EMI, I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, POR, PWM, WDT
Number Of I /o
54
Program Memory Size
256KB (128K x 16)
Program Memory Type
FLASH
Eeprom Size
4K x 8
Ram Size
8K x 8
Voltage - Supply (vcc/vdd)
4.5 V ~ 5.5 V
Data Converters
A/D 8x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
64-TQFP, 64-VQFP
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
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Manufacturer
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17. Timer/Counter 0, 1, 3, 4, and 5 Prescaler
17.1
17.2
17.3
2549M–AVR–09/10
Internal Clock Source
Prescaler Reset
External Clock Source
Timer/Counter 0, 1, 3, 4, and 5 share the same prescaler module, but the Timer/Counters can
have different prescaler settings. The description below applies to all Timer/Counters. Tn is used
as a general name, n = 0, 1, 3, 4, or 5.
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, that is, operates independently of the Clock Select logic of the
Timer/Counter, and it is shared by the Timer/Counter Tn. 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 Tn pin can be used as Timer/Counter clock (clk
Tn pin is sampled once every system clock cycle by the pin synchronization logic. The synchro-
nized (sampled) signal is then passed through the edge detector.
equivalent block diagram of the Tn synchronization and edge detector logic. The registers are
clocked at the positive edge of the internal system clock (
high period of the internal system clock.
The edge detector generates one clk
= 6) edge it detects.
Figure 17-1. Tn/T0 Pin Sampling
CLK_I/O
Tn
clk
I/O
/1024.
D
LE
CLK_I/O
Q
Synchronization
). Alternatively, one of four taps from the prescaler can be used as a
D
Q
ATmega640/1280/1281/2560/2561
Tn
pulse for each positive (CSn2:0 = 7) or negative (CSn2:0
clk
CLK_I/O
I/O
D
). The latch is transparent in the
Figure 17-1
Q
/8, f
CLK_I/O
Edge Detector
/64, f
shows a functional
CLK_I/O
Tn_sync
(To Clock
Select Logic)
Tn
/256, or
). The
169
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