ATmega128A Atmel Corporation, ATmega128A Datasheet - Page 119

• Manufacturer Part Number: ATmega128A
• Manufacturer: Atmel Corporation

Specifications of ATmega128A

• Flash (kbytes): 128 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): 4096
• 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

8151H–AVR–02/11
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 8 bits of the counter, and Counter Low (TCNTnL) containing the lower 8 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 (TOVn) flag 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
TCNTnH (8-bit) TCNTnL (8-bit)
TEMP (8-bit)
T
n
TCNTn (16-bit Counter)
T
n
DATA BUS
is present or not. A CPU write overrides (has priority over) all counter clear or
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).
Direction
Count
T
Clear
n
can be generated from an external or internal clock
“Modes of Operation” on page
Control Logic
TOP
BOTTOM
TOVn
(Int.Req.)
clk
Tn
( From Prescaler )
Clock Select
Detector
ATmega128A
Edge
125.
Tn
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