Schematic and Input/Output pins explain for Arduino UNO R3
The Arduino UNO is a microcontroller board, based on the ATmega8/168/328, UNO R3 major in ATmega328.
Arduino UNO R3 have 14 digital input/output pins (which include about 6 pins PWM output), 6 analog inputs and one 16MHz ceramic resonator,
one USB connection and Power jack, an ICSP header (In Circuit Serial Programming) (like MAX232, RS232 programming).
| Microcontroller | ATmega328 |
| Operating Voltage | 5V |
| Input Voltage (recommended) | 7-12V |
| Input Voltage (limits) | 6-20V |
| Digital I/O Pins | 14 (of which 6 provide PWM output) |
| Analog Input Pins | 6 |
| DC Current per I/O Pin | 40 mA |
| DC Current for 3.3V Pin | 50 mA |
| Flash Memory | 32 KB (ATmega328) of which 0.5 KB used by bootloader |
| SRAM | 2 KB (ATmega328) |
| EEPROM | 1 KB (ATmega328) |
| Clock Speed | 16 MHz |
Input and Output
Each of the 14 digital pins on the UNO R3 can be used as an input or output (thay operate at 5 Volts and provide/receive a maximum of 40mA and has an internal pull-up resistor(disconnected by default) of 20-50 Kohms.), we can using functions as below:
- pinMode()
- digtialWrite()
- digitalRead()
In addition, some pins also have specialized finctions:
- Serial: 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX) TTL serial data. These pins are connected to the corresponding pins of the ATmega8U2 USB-to-TTL Serial chip.
- External Interrupts: 2 and 3. These pins can be configured to trigger an interrupt on a low value, a rising or falling edge, or a change in value.
- PWM: 3, 5, 6, 9, 10, and 11. Provide 8-bit PWM output with the analogWrite() function.
- SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins support SPI communication using the SPI library.
- LED: 13. There is a built-in LED connected to digital pin 13. When the pin is HIGH value, the LED is on, when the pin is LOW, it's off.
The UNO R3 has 6 analog inputs, labeled A0 through A5, each of which provide 10 bits of resolution (i.e. 1024 different values). By default they measure from ground to 5 volts, though is it possible to change the upper end of their range using the AREF pin and the analogReference() function. Additionally, some pins have specialized functionality:
TWI: A4 or SDA pin and A5 or SCL pin. Support TWI communication using the Wire library.
There are a couple of other pins on the board:
AREF. Reference voltage for the analog inputs. Used with analogReference().
Reset. Bring this line LOW to reset the microcontroller. Typically used to add a reset button to shields which block the one on the board.
Note: The Arduino reference design can use an Atmega8, 168, or 328, Current models use an ATmega328, but an Atmega8 is shown in the schematic for reference. The pin configuration is identical on all three processors.
Arduino UNO R3 - Schematic
Download EAGLE files:
http://arduino.cc/en/uploads/Main/arduino_Uno_Rev3-02-TH.zip
Download Schematic file:
http://arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf
ATmega168/328-Arduino Pin Mapping
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