Arduino Mega 2560
Overview
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.
Schematic & Reference Design
EAGLE files: arduino-mega2560-reference-design.zip
Schematic: arduino-mega2560-schematic.pdf
Summary
Microcontroller
ATmega2560
Operating Voltage
5V
Input Voltage (recommended) 7-12V
Input Voltage (limits)
6-20V
Digital I/O Pins
54 (of which 14 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 Mega2560 differs from all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it
features the Atmega8U2 programmed as a USB-to-serial converter.
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. The regulated power supply used to power the microcontroller and other components on the board. This can come
either from VIN via an on-board regulator, or be supplied by USB or another regulated 5V supply.
3V3. A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
GND. Ground pins.
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 ATmega8U2 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: 0 to 13. 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.
I 2 C: 20 (SDA) and 21 (SCL). Support I 2C (TWI) communication using the Wire library (documentation on the
Wiring website). Note that these pins are not in the same location as the I 2C 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 ATmega8U2
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 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 I2C (TWI) and SPI communication. The Arduino software includes a Wire library to
simplify use of the I2C bus; see the documentation on the Wiring website for details. For SPI communication, use the SPI
library.
Programming
The Arduino Mega can be programmed with the Arduino software (download). For details, see the reference and tutorials.
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; see these instructions for details.
The ATmega8U2 firmware source code is available in the Arduino repository. The ATmega8U2 is loaded with a DFU
bootloader, which can be activated by connecting the solder jumper on the back of the board (near the map of Italy) and
then resetting the 8U2. 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). See this user-contributed tutorial for more information.
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; see this forum thread for details.
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.
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 I 2C is not located on the same pins on the Mega (20 and 21) as the Duemilanove / Diecimila
(analog inputs 4 and 5).
Arduino Mega 2560 Reference Design
TM
Reference Designs ARE PROVIDED "AS IS" AND "WITH ALL FAULTS". Arduino DISCLAIMS ALL OTHER WARRANTIES, EXPRESS OR IMPLIED,
REGARDING PRODUCTS, INCLUDING BUT NOT LIMITED TO, ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
Arduino may make changes to specifications and product descriptions at any time, without notice. The Customer must not
rely on the absence or characteristics of any features or instructions marked "reserved" or "undefined." Arduino reserves
these for future definition and shall have no responsibility whatsoever for conflicts or incompatibilities arising from future changes to them.
The product information on the Web Site or Materials is subject to change without notice. Do not finalize a design with this information.
+5V
PL1
PL3
PL5
PL7
PG1
PD7
ADCH
8
7
6
5
4
3
2
1
PL7
PL6
PL5
PL4
PL3
PL2
PL1
PL0
pwm
pwm
pwm
ADC15
ADC14
ADC13
ADC12
ADC11
ADC10
ADC9
ADC8
82
83
84
85
86
87
88
89
+5V+3V3
POWER
1
2
3
4
5
6
pwm
pwm
pwm
pwm
PH6
PH5
PH4
PH3
TXD2
RXD2
TS42
RESET
27
18
17
16
15
14
13
12
PK7(ADC15/PCINT23)
PK6(ADC14/PCINT22)
PK5(ADC13/PCINT21)
PK4(ADC12/PCINT20)
PK3(ADC11/PCINT19)
PK2(ADC10/PCINT18)
PK1(ADC9/PCINT17)
PK0(ADC8/PCINT16)
PJ7
PJ6(PCINT15)
PJ5(PCINT14)
PJ4(PCINT13)
PJ3(PCINT12)
PJ2(XCK3/PCINT11)
PJ1(TXD3/PCINT10)
PJ0(RXD3/PCINT9)
PH7(T4)
PH6(OC2B)
PH5(OC4C)
PH4(OC4B)
PH3(OC4A)
PH2(XCK2)
PH1(TXD2)
PH0(RXD2)
(T0)PD7
(T1)PD6
(XCK1)PD5
(ICP1)PD4
(TXD1/INT3)PD3
(RXD1/INT2)PD2
(SDA/INT1)PD1
(SCL/INT0)PD0
(CLKO/ICP3/INT7)PE7
(T3/INT6)PE6
(OC3C/INT5)PE5
(OC3B/INT4)PE4
(OC3A/AIN1)PE3
(XCK0/AIN0)PE2
(TXD0)PE1
(RXD0/PCIN8)PE0
(ADC7/TDI)PF7
(ADC6/TDO)PF6
(ADC5/TMS)PF5
(ADC4/TCK)PF4
(ADC3)PF3
(ADC2)PF2
(ADC1)PF1
(ADC0)PF0
(OC0B)PG5
(TOSC1)PG4
(TOSC2)PG3
(ALE)PG2
(RD)PG1
(WR)PG0
50
49
48
47
46
45
44
43
PD7
9
8
7
6
5
4
3
2
PE1
PE0
pwm
pwm
pwm
(TX0)
(RX0)
PH4
PH3
PE3
PG5
PE5
PE4
PE1
PE0
8
7
6
5
4
3
2
1
14
15
16
17
18
19
20
21
8
7
6
5
4
3
2
1
7
6
5
4
3
2
1
0
8
7
6
5
4
3
2
1
C14
22p
GND
2
1
16MHz
Q2
2
1
16MHz
Q1
MOSI2
2
COMMUNICATION
7
RN2B 22R
3
1
2
3
4
6
RN2C 22R
USBVCC
22R
8 RN2A
1
500mA
DD+
22R
5 RN2D
4
1
8
R2
RD- 1M
RD+
2
7
4
XT1
16MHz
+5V
GND
5
32
27
31
30
29
28
EXP
1
21
20
19
18
17 MISO2
16 MOSI2
15 SCK2
14
(PCINT7/OC0A/OC1C)PB7
(PCINT6)PB6
(PCINT5)PB5
(T1/PCINT4)PB4
(PD0/MISO/PCINT3)PB3
(PDI/MOSI/PCINT2)PB2
(SCLK/PCINT1)PB1
(SS/PCINT0)PB0
RESET(PC1/DW)
XTAL2(PC0)
XTAL1
AVCC
UCAP
UVCC
DD+
UGND
PAD
22
23
25
26
5
(INT4/ICP1/CLK0)PC7
(OC1A/PCINT8)PC6
(PCINT9/OC1B)PC5
(PCINT10)PC4
(AIN2/PCINT11)PC2
VCC
GND
13
12
11
TXL
10
RXL
9 M8RXD
8 M8TXD
7
6
(CTS/HWB/AIN6/TO/INT7)PD7
(RTS/AIN5/INT6)PD6
(XCK/AIN4/PCINT12)PD5
(INT5/AIN3)PD4
(TXD1/INT3)PD3
(RXD1/AIN1/INT2)PD2
(AIN0/INT1)PD1
(OC0B/INT0)PD0
2
PE0
PE1
7
RN4B 1k
3
7
C11
100n
GND
CMP
+3V3
5
6
3
7
2
LM358D
IC5A
1
LM358D
GND
C12
100n
GND
IC5B
GATE_CMD
+5V
USBVCC
+5V
+5V 1
3
2
T2
FDN340P
IN
OUT
5
EN
GND NC/FB
4
+3V3
+3V3
GND
GND
RESET
GND
3
6
RN4C 1k
TX
YELLOW
4
M8RXD
M8TXD
1
8
RN4A 1k
VIN
2
ATMEGA8U2-MU
2
GND
5
RN1D 10K
+5V
DTR
GROUND
RN5D 10K
4
2
XT1R 1
VUCAP
USBVCC
RDRD+
UGND
1u
C10
100n
C9
RN3B 1k
ADCL
XT2
4
3
L1
RN3A 1k
24
Y2
BLM21
PWML
1
RESET-EN
IC4
RESET2
C8
100n
F1
XVCC
GND
PG5 pwm
PG2
PG1
PG0
C15
22p
C16
22p
GND
C17
22p
6
RN1C 10K
7
1
2
pwm
pwm
pwm
pwm
pwm
pwm
pwm
pwm
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
90
91
92
93
94
95
96
97
1
29
28
70
52
51
GND
X2
TXD3
RXD3
TXD2
RXD2
TXD1
RXD1
2
4
6
ICSP
PWMH
SDA
SCL
PE5
PE4
PE3
1
MISO2
3
SCK2
RESET2 5
ATMEGA1280-16AU
GND
4
3
5
2
1
79
69
68
67
66
65
64
63
PL7
PL6
PL5(OC5C)
PL4(OC5B)
PL3(OC5A)
PL2(T5)
PL1(ICP5)
PL0(ICP4)
ICSP1
2
VIN
TXD3
RXD3
GND
42
41
40
39
38
37
36
35
pwm
pwm
+5V
13
12
11
10
9
8
C7
52
50
48
46
44
42
40
38
PH6
PH5
GND
100n
(SCK) PB1
(MISO) PB3
PC7
PC6
PC5
PC4
PC3
PC2
PC1
PC0
8
7
6
5
4
3
2
1
XTAL2
2
2
4
6
8
10
12
14
16
60
59
58
57
56
55
54
53
(MISO)
(MOSI)
(SCK)
AREF
GND
XT2
1
1
3
5
7
9
11
13
15
PB3
PB2
PB1
PB0
pwm
pwm
pwm
pwm
GND
JP4
XTAL1
36
34
32
30
28
26
24
22
8
PB0 (SS)
PB2 (MOSI)
PL0
PL2
PL4
PL6
PG0
PG2
PB7
PB6
PB5
PB4
PC1
PC3
PC5
PC7
PA6
PA4
PA2
PA0
4
53
51
49
47
45
43
41
39
XIOL
(A15)PC7
(A14)PC6
(A13)PC5
(A12)PC4
(A11)PC3
(A10)PC2
(A9)PC1
(A8)PC0
26
25
24
23
22
21
20
19
2
4
6
8
10
12
14
16
1
XT1
USB boot En
UBOOT
GND
(OC0A/OC1C/PCINT7)PB7
(OC1B/PCINT6)PB6
(OC1A/PCINT5)PB5
(OC2A/PCINT4)PB4
(MISO/PCINT3)PB3
(MOSI/PCINT2)PB2
(SCK/PCINT1)PB1
(SS/PCINT0)PB0
1
3
5
7
9
11
13
15
JP3
10K
8 RN5A
1
100n
VCC
VCC
VCC
VCC
GND
GND
GND
GND
XIOH
JP2
1
100n C13
100n
AREF
AVCC
AGND
PC0
PC2
PC4
PC6
PA7
PA5
PA3
PA1
JP1
1
UGND
100n
GND
10
31
61
80
11
32
62
81
C6
XTAL1
37
35
33
31
29
27
25
23
PGB1010604
C5
98
100
99
PA7
PA6
PA5
PA4
PA3
PA2
PA1
PA0
Z2
C4
+5V
XTAL2
71
72
73
74
75
76
77
78
PGB1010604
34
(AD7)PA7
(AD6)PA6
(AD5)PA5
(AD4)PA4
(AD3)PA3
(AD2)PA2
(AD1)PA1
(AD0)PA0
(MOSI)
USB
100n
33
XTAL1R
RESET
PB2
Z1
AREF
C3
30
XTAL2
AREF
R3
27R
XTAL1
2
4
6
SCL
SDA
P$2
P$1
GND
16MHz
1
3
5
ICSP
IC3
R1
1M
PB3
PB1
RESET
(MISO)
(SCK)
GND
GND
RESET
Y1
RESET
4
ICSP
1
R4
27R
5
+5V
6
GND
YELLOW
RN3D 1k
L
22p
P$1
1
GND
PC2
47u
GREEN
ON
USHIELD P$2
ADJ
6
+5V
C1
GND
3
+5V
3
8
VO
RN3C 1k
2
100n
GND
GND
VI
C2
+
PWRIN
3
RESET
GND
D1
M7
PC1
47u
+
2
2
1
1
3
+5V
GND
IC2
MC33269D-5.0
VIN
3
+5V
GND
1
MC33269ST-5.0T3
RN1B 10K
4
2
IN OUT
RN5B 10K RN5C 10K
IC1
RN1A 10K
3
5
RX
RN4D 1k
YELLOW
+5V