ATMEGA8A-PU Atmel, ATMEGA8A-PU Datasheet - Page 71

• Manufacturer Part Number: ATMEGA8A-PU
• Description: MCU AVR 8K FLASH 16MHZ 28-PDIP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA8A-PU

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 16MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 23
• Program Memory Size: 8KB (4K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 512 x 8
• Ram Size: 1K x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 6x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 28-DIP (0.300", 7.62mm)
• Processor Series: ATMEGA8x
• Core: AVR8
• Data Bus Width: 8 bit
• Data Ram Size: 1 KB
• Interface Type: SPI, TWI, USART
• Maximum Clock Frequency: 16 MHz
• Number Of Programmable I/os: 23
• Number Of Timers: 3
• Maximum Operating Temperature: + 85 C
• Mounting Style: Through Hole
• 3rd Party Development Tools: EWAVR, EWAVR-BL
• Development Tools By Supplier: ATAVRDRAGON, ATSTK500, ATSTK600, ATAVRISP2, ATAVRONEKIT
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 10 bit, 6 Channel
• Package: 28PDIP
• Device Core: AVR
• Family Name: ATmega
• Maximum Speed: 16 MHz
• Operating Supply Voltage: 3.3|5 V
• Controller Family/series: AVR MEGA
• No. Of I/o's: 23
• Eeprom Memory Size: 512Byte
• Ram Memory Size: 1KB
• Cpu Speed: 16MHz
• Rohs Compliant: Yes
• For Use With: ATSTK600 - DEV KIT FOR AVR/AVR32ATSTK500 - PROGRAMMER AVR STARTER KIT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

14.3
14.4
14.5
8159D–AVR–02/11
Timer/Counter Clock Sources
Counter Unit
Operation
defines in a program, the precise form must be used i.e. TCNT0 for accessing Timer/Counter0
counter value and so on.
The definitions in
Table 14-1.
The Timer/Counter can be clocked by an internal or an external clock source. The clock source
is selected by the clock select logic which is controlled by the clock select (CS02:0) bits located
in the Timer/Counter Control Register (TCCR0). For details on clock sources and prescaler, see
“Timer/Counter0 and Timer/Counter1 Prescalers” on page
The main part of the 8-bit Timer/Counter is the programmable counter unit.
block diagram of the counter and its surroundings.
Figure 14-2. Counter Unit Block Diagram
Signal description (internal signals):
The counter is incremented at each timer clock (clk
or internal clock source, selected by the clock select bits (CS02:0). When no clock source is
selected (CS02:0 = 0) the timer is stopped. However, the TCNT0 value can be accessed by the
CPU, regardless of whether clk
counter clear or count operations.
The counting direction is always up (incrementing), and no counter clear is performed. The
counter simply overruns when it passes its maximum 8-bit value (MAX = 0xFF) and then restarts
from the bottom (0x00). In normal operation the Timer/Counter Overflow Flag (TOV0) will be set
in the same timer clock cycle as the TCNT0 becomes zero. The TOV0 Flag in this case behaves
like a ninth bit, except that it is only set, not cleared. However, combined with the timer overflow
BOTTOM
MAX
count
clk
max
Tn
DATA BUS
TCNTn
Definitions
The counter reaches the BOTTOM when it becomes 0x00
The counter reaches its MAXimum when it becomes 0xFF (decimal 255)
Table 14-1
are also used extensively throughout this datasheet.
count
Increment TCNT0 by 1.
Timer/Counter clock, referred to as clk
Signalize that TCNT0 has reached maximum value.
T0
is present or not. A CPU write overrides (has priority over) all
Control Logic
max
TOVn
(Int. Req.)
clk
T0
Tn
). clk
T0
75.
can be generated from an external
Clock Select
( From Prescaler )
Detector
Edge
T0
in the following.
ATmega8A
Figure 14-2
Tn
shows a
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