ATmega128A Atmel Corporation, ATmega128A Datasheet - Page 152

• 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

17.6
8151H–AVR–02/11
Compare Match Output Unit
equals the OCR2 value, the compare match will be missed, resulting in incorrect waveform gen-
eration. Similarly, do not write the TCNT2 value equal to BOTTOM when the counter is
downcounting.
The setup of the OC2 should be performed before setting the Data Direction Register for the port
pin to output. The easiest way of setting the OC2 value is to use the Force Output Compare
(FOC2) strobe bits in normal mode. The OC2 Register keeps its value even when changing
between waveform generation modes.
Be aware that the COM21:0 bits are not double buffered together with the compare value.
Changing the COM21:0 bits will take effect immediately.
The Compare Output mode (COM21:0) bits have two functions. The waveform generator uses
the COM21:0 bits for defining the output compare (OC2) state at the next compare match. Also,
the COM21:0 bits control the OC2 pin output source.
of the logic affected by the COM21:0 bit setting. The I/O registers, I/O bits, and I/O pins in the
figure are shown in bold. Only the parts of the general I/O Port Control Registers (DDR and
PORT) that are affected by the COM21:0 bits are shown. When referring to the OC2 state, the
reference is for the internal OC2 Register, not the OC2 pin. If a System Reset occur, the OC2
Register is reset to “0”.
Figure 17-4. Compare Match Output Unit, Schematic
The general I/O port function is overridden by the output compare (OC2) from the waveform
generator if either of the COM21:0 bits are set. However, the OC2 pin direction (input or output)
is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction Regis-
ter bit for the OC2 pin (DDR_OC2) must be set as output before the OC2 value is visible on the
pin. The port override function is independent of the Waveform Generation mode.
The design of the output compare pin logic allows initialization of the OC2 state before the out-
put is enabled. Note that some COM21:0 bit settings are reserved for certain modes of
operation.
See “Register Description” on page 159.
COMn1
COMn0
FOCn
clk
I/O
Waveform
Generator
D
D
D
PORT
DDR
OCn
Q
Q
Q
Figure 17-4
1
0
shows a simplified schematic
ATmega128A
OCn
Pin
152