ATMEGA64A-ANR Atmel, ATMEGA64A-ANR Datasheet - Page 117

• Manufacturer Part Number: ATMEGA64A-ANR
• Description: IC MCU AVR 64K FLASH 64TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA64A-ANR

• 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: 53
• Program Memory Size: 64KB (32K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 2K x 8
• Ram Size: 4K x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

8160C–AVR–07/09
Figure 15-2. Counter Unit Block Diagram
Signal description (internal signals):
The 16-bit counter is mapped into two 8-bit I/O memory locations: Counter High (TCNTnH) con-
taining the upper eight bits of the counter, and Counter Low (TCNTnL) containing the lower eight
bits. The TCNTnH Register can only be indirectly accessed by the CPU. When the CPU does an
access to the TCNTnH I/O location, the CPU accesses the high byte temporary register (TEMP).
The temporary register is updated with the TCNTnH value when the TCNTnL is read, and
TCNTnH is updated with the temporary register value when TCNTnL is written. This allows the
CPU to read or write the entire 16-bit counter value within one clock cycle via the 8-bit data bus.
It is important to notice that there are special cases of writing to the TCNTn Register when the
counter is counting that will give unpredictable results. The special cases are described in the
sections where they are of importance.
Depending on the mode of operation used, the counter is cleared, incremented, or decremented
at each Timer Clock (clk
source, selected by the Clock Select bits (CSn2:0). When no clock source is selected (CSn2:0 =
0) the timer is stopped. However, the TCNTn value can be accessed by the CPU, independent
of whether clk
count operations.
The counting sequence is determined by the setting of the Waveform Generation mode bits
(WGMn3:0) located in the Timer/Counter Control Registers A and B (TCCRnA and TCCRnB).
There are close connections between how the counter behaves (counts) and how waveforms
are generated on the Output Compare outputs OCnx. For more details about advanced counting
sequences and waveform generation, see
The Timer/Counter Overflow Flag (TOVn) is set according to the mode of operation selected by
the WGMn3:0 bits. TOVn can be used for generating a CPU interrupt.
Count
Direction
Clear
clk
TOP
BOTTOM
T
n
TCNTnH (8-bit)
TEMP (8-bit)
T
n
TCNTn (16-bit Counter)
is present or not. A CPU write overrides (has priority over) all counter clear or
DATA BUS
TCNTnL (8-bit)
T
n
(8-bit)
). The clk
Increment or decrement TCNTn by 1.
Select between increment and decrement.
Clear TCNTn (set all bits to zero).
Timer/counter clock.
Signalize that TCNTn has reached maximum value.
Signalize that TCNTn has reached minimum value (zero).
T
Direction
n
Count
Clear
can be generated from an external or internal clock
“Modes of Operation” on page
Control Logic
TOP
BOTTOM
TOVn
(Int.Req.)
clk
Tn
Clock Select
( From Prescaler )
Detector
Edge
ATmega64A
123.
Tn
117