The Mega 2560 is a micro-controller board base on the CH340. It has 54 digital input/output pins (of which 15 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 need to support the micro-controller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get start. The Mega is compatible with most shields design for the Duemilanove or Diecimila.
The Mega 2560 is an update to the 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 CH340 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.
1.0 pinout: added SDA and SCL pins that are near to the AREF pin and two other new pins place near to the RESET pin, the IOREF that allow the shields to adapt to the voltage provide from the board. In future, shields will be compatible both with the board that use the AVR, which operate with 5V and with the Due that operate with 3.3V. The second one is a not connect to pin, that is reserved for future purposes.
Stronger RESET circuit.
Atmega 16U2 replace the 8U
The power pins are as follows:
VIN – The input voltage to the 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 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.
The CH340 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 EEPORM libary).
Each of the 54 digital pins on the Mega can be use 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.
Serial : serial0: (RX) and 1 (TX), Serial1: 19 (RX) and 18 (TX), Serial2: 17 (RX) and 16 (TX); Serial3: 15 (RX) and 14 (TX). Used to receive (RX) and transmit (TX) TTL serial data. Pins 0 and 1 are also connect 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 configure 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 connect 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 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.
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.
The Mega2560 has a number of facilities for communicating with a computer, another , or other microcontrollers. The CH340 provides four hardware UARTs for TTL (5V) serial communication. An CH340 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 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 transmit via the CH340 chip and USB connection to the computer (but not for serial communication on pins 0 and 1).
A SoftwareSerial libary allows for serial communication on any of the Mega2560’s digital pins.
The CH340 also supports TWI and SPI communication. The software includes a Wire library to simplify use of the TWI bus; see the documentation for details. For SPI communication, use the SPI libary.
The ATmega2560 on the 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 hearder files).
You can also bypass the bootloader and program the microcontroller through the ICSP (In-Circuit Serial Programming) header using ISP or similar; see these instructions for details. The CH340 firmware source code is available in the repository.
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 boot-loader). See this user-contribute tutorial for more information.
Rather then requiring a physical press of the reset button before an upload, the Mega 2560 is design in a way that allows it to be reset by software running on a connect computer. One of the hardware flow control lines (DTR) of the ATmega8U2 is connect to the reset line of the ATmega2560 via a 100 nano-farad capacitor. When this line is assert (taken low); the reset line drops long enough to reset the chip. The software uses this capability to allow you to upload code by simply pressing the upload button in the environment. This means that the boot-loader can have a shorter timeout, as the lowering of DTR can be well coordinate with the start of the upload.
This setup has other implications. When the Mega 2560 is connect 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 boot-loader is running on the Mega 2560. While it is program 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 open. 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; see this forum thread for details.
The Mega 2560 has a re-settable poly-fuse that protects your computer’s USB ports from shorts and over-current. Although most computers provide their own internal protection, the fuse provides an extra layer of protection. If more than 500 mA is apply to the USB port; the fuse will automatically break the connection until the short or overload is remove.
The maximum length and width of the Mega 2560 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 attach 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 design to be compatible with most shields design 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 locatE 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 locatE on the same pins on the Mega (20 and 21) as the Duemilanove / Diecimila (analog inputs 4 and 5).
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