Arduino Mega 2560
Overview
Arduino Mega 2560 Development Board |
The Arduino Mega 2560 is a microcontroller board based on the ATmega2560 (datasheet). It has 54 digital input/output pins (of which 14 can be used as PWM outputs), 16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz
crystal oscillator, a USB connection, a power jack, an ICSP header, and
a reset button. It contains everything needed to support the
microcontroller; simply connect it to a computer with a USB cable or
power it with a AC-to-DC adapter or battery to get started. The Mega is
compatible with most shields designed for the Arduino Duemilanove or
Diecimila.
The Mega 2560 is an update to the Arduino Mega, which it replaces.
The Mega2560 differs from all preceding boards
in that it does not use the FTDI USB-to-serial driver chip. Instead, it
features the ATmega16U2 (ATmega8U2 in the revision 1 and revision 2 boards) programmed as a USB-to-serial converter.
Revision 2
of the Mega2560 board has a resistor pulling the 8U2 HWB line to ground, making it easier to put into DFU mode.
Revision 3
of the board has the following new features:
- 1.0 pinout: added SDA and SCL pins that are near to the AREF pin and two other new pins placed near to the RESET pin, the IOREF that allow the shields to adapt to the voltage provided from the board. In future, shields will be compatible both with the board that use the AVR, which operate with 5V and with the Arduino Due that operate with 3.3V. The second one is a not connected pin, that is reserved for future purposes.
- Stronger RESET circuit.
- Atmega 16U2 replace the 8U2.
Schematic, Reference Design & Pin Mapping
EAGLE files: arduino-mega2560_R3-reference-design.zip
Schematic: arduino-mega2560_R3-schematic.pdf
Pin Mapping: PinMap2560 page
Summary
Microcontroller | ATmega2560 |
Operating Voltage | 5V |
Input Voltage (recommended) | 7-12V |
Input Voltage (limits) | 6-20V |
Digital I/O Pins | 54 (of which 15 provide PWM output) |
Analog Input Pins | 16 |
DC Current per I/O Pin | 40 mA |
DC Current for 3.3V Pin | 50 mA |
Flash Memory | 256 KB of which 8 KB used by bootloader |
SRAM | 8 KB |
EEPROM | 4 KB |
Clock Speed | 16 MHz |
Power
The Arduino Mega can be powered via the USB connection or with an
external power supply. The power source is selected automatically.
External (non-USB) power can come either from
an AC-to-DC adapter (wall-wart) or battery. The adapter can be
connected by plugging a 2.1mm center-positive plug into the board's
power jack. Leads from a battery can be inserted in the Gnd and Vin pin
headers of the POWER connector.
The board can operate on an external supply of 6
to 20 volts. If supplied with less than 7V, however, the 5V pin may
supply less than five volts and the board may be unstable. If using
more than 12V, the voltage regulator may overheat and damage the board.
The recommended range is 7 to 12 volts.
The power pins are as follows:
- VIN. The input voltage to the Arduino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.
- 5V. This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
- 3V3. A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
- GND. Ground pins.
- IOREF. This pin on the Arduino board provides the voltage reference with which the microcontroller operates. A properly configured shield can read the IOREF pin voltage and select the appropriate power source or enable voltage translators on the outputs for working with the 5V or 3.3V.
Click to view the Atmega 2560 Pin Mapping.
Memory
The ATmega2560 has 256 KB of flash
memory for storing code (of which 8 KB is used for the bootloader), 8 KB
of SRAM and 4 KB of EEPROM (which can be read and written with the EEPROM library).
Input and Output
Each of the 54 digital pins on the Mega can be used as an input or output, using pinMode(), digitalWrite(), and digitalRead()
functions. They operate at 5 volts. Each pin can provide or receive a
maximum of 40 mA and has an internal pull-up resistor (disconnected by
default) of 20-50 kOhms. In addition, some pins have specialized
functions:
- Serial: 0 (RX) and 1 (TX); Serial 1: 19 (RX) and 18 (TX); Serial 2: 17 (RX) and 16 (TX); Serial 3: 15 (RX) and 14 (TX). Used to receive (RX) and transmit (TX) TTL serial data. Pins 0 and 1 are also connected to the corresponding pins of the ATmega16U2 USB-to-TTL Serial chip.
- External Interrupts: 2 (interrupt 0), 3 (interrupt 1), 18 (interrupt 5), 19 (interrupt 4), 20 (interrupt 3), and 21 (interrupt 2). These pins can be configured to trigger an interrupt on a low value, a rising or falling edge, or a change in value. See the attachInterrupt() function for details.
- PWM: 2 to 13 and 44 to 46. Provide 8-bit PWM output with the analogWrite() function.
- SPI: 50 (MISO), 51 (MOSI), 52 (SCK), 53 (SS). These pins support SPI communication using the SPI library. The SPI pins are also broken out on the ICSP header, which is physically compatible with the Uno, Duemilanove and Diecimila.
- 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.
- TWI: 20 (SDA) and 21 (SCL). Support TWI communication using the Wire library. Note that these pins are not in the same location as the TWI pins on the Duemilanove or Diecimila.
The Mega2560 has 16 analog inputs,
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
analogReference() function.
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.
Communication
The Arduino Mega2560 has a number of facilities for communicating
with a computer, another Arduino, or other microcontrollers. The ATmega2560 provides four hardware UARTs for TTL (5V) serial communication. An ATmega16U2 (ATmega
8U2 on the revision 1 and revision 2 boards) on the board channels one
of these over USB and provides a virtual com port to software on the
computer (Windows machines will need a .inf file, but OSX and Linux
machines will recognize the board as a COM port automatically. The
Arduino software includes a serial monitor which allows simple textual
data to be sent to and from the board. The RX and TX LEDs on the board will flash when data is being transmitted via the ATmega8U2/ATmega16U2 chip and USB connection to the computer (but not for serial communication on pins 0 and 1).
A SoftwareSerial library allows for serial communication on any of the Mega2560's digital pins.
The ATmega2560 also supports TWI and SPI communication. The Arduino software includes a Wire library to simplify use of the TWI bus; see the documentation for details. For SPI communication, use the SPI library.
Programming
The Arduino Mega can be programmed with the Arduino software (download).
The ATmega2560 on the Arduino Mega comes preburned with a bootloader
that allows you to upload new code to it without the use of an external
hardware programmer. It communicates using the original STK500 protocol (reference, C header files).
You can also bypass the bootloader and program the microcontroller through the ICSP (In-Circuit Serial Programming) header.
The ATmega16U2 (or 8U2 in the rev1 and rev2 boards) firmware source code is available in the Arduino repository. The ATmega16U2/8U2 is loaded with a DFU bootloader, which can be activated by:
- On Rev1 boards: connecting the solder jumper on the back of the board (near the map of Italy) and then resetting the 8U2.
- On Rev2 or later boards: there is a resistor that pulling the 8U2/16U2 HWB line to ground, making it easier to put into DFU mode. You can then use Atmel's FLIP software (Windows) or the DFU programmer (Mac OS X and Linux) to load a new firmware. Or you can use the ISP header with an external programmer (overwriting the DFU bootloader).
Automatic (Software) Reset
Rather then requiring a physical press of the reset button before an
upload, the Arduino Mega2560 is designed in a way that allows it to be
reset by software running on a connected computer. One of the hardware
flow control lines (DTR) of the ATmega8U2 is connected to the reset line of the ATmega2560
via a 100 nanofarad capacitor. When this line is asserted (taken low),
the reset line drops long enough to reset the chip. The Arduino
software uses this capability to allow you to upload code by simply
pressing the upload button in the Arduino environment. This means that
the bootloader can have a shorter timeout, as the lowering of DTR can be
well-coordinated with the start of the upload.
This setup has other implications. When the
Mega2560 is connected to either a computer running Mac OS X or Linux, it
resets each time a connection is made to it from software (via USB).
For the following half-second or so, the bootloader is running on the
Mega2560. While it is programmed to ignore malformed data (i.e.
anything besides an upload of new code), it will intercept the first few
bytes of data sent to the board after a connection is opened. If a
sketch running on the board receives one-time configuration or other
data when it first starts, make sure that the software with which it
communicates waits a second after opening the connection and before
sending this data.
The Mega2560 contains a trace that can be cut
to disable the auto-reset. The pads on either side of the trace can be
soldered together to re-enable it. It's labeled "RESET-EN". You may
also be able to disable the auto-reset by connecting a 110 ohm resistor
from 5V to the reset line.
USB Overcurrent Protection
The Arduino Mega2560 has a resettable polyfuse that protects your computer's USB ports from shorts and overcurrent. Although most computers provide their own internal protection, the fuse provides an extra layer of protection. If more than 500 mA is applied to the USB port, the fuse will automatically break the connection until the short or overload is removed.Arduino Mega, With Labels Indicating Pins |
Physical Characteristics and Shield Compatibility
The maximum length and width of the Mega2560 PCB are 4 and 2.1 inches
respectively, with the USB connector and power jack extending beyond
the former dimension. Three screw holes allow the board to be attached
to a surface or case. Note that the distance between digital pins 7 and
8 is 160 mil (0.16"), not an even multiple of the 100 mil spacing of
the other pins.
The Mega2560 is designed to be compatible with
most shields designed for the Uno, Diecimila or Duemilanove. Digital
pins 0 to 13 (and the adjacent AREF and GND pins), analog inputs 0 to 5,
the power header, and ICSP header are all in equivalent locations.
Further the main UART (serial port) is located on the same pins (0 and
1), as are external interrupts 0 and 1 (pins 2 and 3 respectively). SPI
is available through the ICSP header on both the Mega2560 and
Duemilanove / Diecimila. Please note that I2C is not located on the same pins on the Mega (20 and 21) as the Duemilanove / Diecimila (analog inputs 4 and 5).
Information source : arduino.cc
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