atmega2560 Pin Mapping

Differences In External Interrupts
The external interrupts are associated with specific digital pins on each chip type, the following table taken from the attachInterrupt reference page lists the available external interrupts and the associated Arduino pin on each chip -

Board	int.0	int.1	int.2	int.3	int.4	int.5
Uno, Ethernet, Mini	2	3
Mega2560	2	3	21	20	19	18
Leonardo, Micro	3	2	0	1

Arduino Mega 2560 PIN mapping table

Pin Number	Pin Name	Mapped Pin Name
1	PG5 ( OC0B )	Digital pin 4 (PWM)
2	PE0 ( RXD0/PCINT8 )	Digital pin 0 (RX0)
3	PE1 ( TXD0 )	Digital pin 1 (TX0)
4	PE2 ( XCK0/AIN0 )
5	PE3 ( OC3A/AIN1 )	Digital pin 5 (PWM)
6	PE4 ( OC3B/INT4 )	Digital pin 2 (PWM)
7	PE5 ( OC3C/INT5 )	Digital pin 3 (PWM)
8	PE6 ( T3/INT6 )
9	PE7 ( CLKO/ICP3/INT7 )
10	VCC	VCC
11	GND	GND
12	PH0 ( RXD2 )	Digital pin 17 (RX2)
13	PH1 ( TXD2 )	Digital pin 16 (TX2)
14	PH2 ( XCK2 )
15	PH3 ( OC4A )	Digital pin 6 (PWM)
16	PH4 ( OC4B )	Digital pin 7 (PWM)
17	PH5 ( OC4C )	Digital pin 8 (PWM)
18	PH6 ( OC2B )	Digital pin 9 (PWM)
19	PB0 ( SS/PCINT0 )	Digital pin 53 (SS)
20	PB1 ( SCK/PCINT1 )	Digital pin 52 (SCK)
21	PB2 ( MOSI/PCINT2 )	Digital pin 51 (MOSI)
22	PB3 ( MISO/PCINT3 )	Digital pin 50 (MISO)
23	PB4 ( OC2A/PCINT4 )	Digital pin 10 (PWM)
24	PB5 ( OC1A/PCINT5 )	Digital pin 11 (PWM)
25	PB6 ( OC1B/PCINT6 )	Digital pin 12 (PWM)
26	PB7 ( OC0A/OC1C/PCINT7 )	Digital pin 13 (PWM)
27	PH7 ( T4 )
28	PG3 ( TOSC2 )
29	PG4 ( TOSC1 )
30	RESET	RESET
31	VCC	VCC
32	GND	GND
33	XTAL2	XTAL2
34	XTAL1	XTAL1
35	PL0 ( ICP4 )	Digital pin 49
36	PL1 ( ICP5 )	Digital pin 48
37	PL2 ( T5 )	Digital pin 47
38	PL3 ( OC5A )	Digital pin 46 (PWM)
39	PL4 ( OC5B )	Digital pin 45 (PWM)
40	PL5 ( OC5C )	Digital pin 44 (PWM)
41	PL6	Digital pin 43
42	PL7	Digital pin 42
43	PD0 ( SCL/INT0 )	Digital pin 21 (SCL)
44	PD1 ( SDA/INT1 )	Digital pin 20 (SDA)
45	PD2 ( RXDI/INT2 )	Digital pin 19 (RX1)
46	PD3 ( TXD1/INT3 )	Digital pin 18 (TX1)
47	PD4 ( ICP1 )
48	PD5 ( XCK1 )
49	PD6 ( T1 )
50	PD7 ( T0 )	Digital pin 38
51	PG0 ( WR )	Digital pin 41
52	PG1 ( RD )	Digital pin 40
53	PC0 ( A8 )	Digital pin 37
54	PC1 ( A9 )	Digital pin 36
55	PC2 ( A10 )	Digital pin 35
56	PC3 ( A11 )	Digital pin 34
57	PC4 ( A12 )	Digital pin 33
58	PC5 ( A13 )	Digital pin 32
59	PC6 ( A14 )	Digital pin 31
60	PC7 ( A15 )	Digital pin 30
61	VCC	VCC
62	GND	GND
63	PJ0 ( RXD3/PCINT9 )	Digital pin 15 (RX3)
64	PJ1 ( TXD3/PCINT10 )	Digital pin 14 (TX3)
65	PJ2 ( XCK3/PCINT11 )
66	PJ3 ( PCINT12 )
67	PJ4 ( PCINT13 )
68	PJ5 ( PCINT14 )
69	PJ6 ( PCINT 15 )
70	PG2 ( ALE )	Digital pin 39
71	PA7 ( AD7 )	Digital pin 29
72	PA6 ( AD6 )	Digital pin 28
73	PA5 ( AD5 )	Digital pin 27
74	PA4 ( AD4 )	Digital pin 26
75	PA3 ( AD3 )	Digital pin 25
76	PA2 ( AD2 )	Digital pin 24
77	PA1 ( AD1 )	Digital pin 23
78	PA0 ( AD0 )	Digital pin 22
79	PJ7
80	VCC	VCC
81	GND	GND
82	PK7 ( ADC15/PCINT23 )	Analog pin 15
83	PK6 ( ADC14/PCINT22 )	Analog pin 14
84	PK5 ( ADC13/PCINT21 )	Analog pin 13
85	PK4 ( ADC12/PCINT20 )	Analog pin 12
86	PK3 ( ADC11/PCINT19 )	Analog pin 11
87	PK2 ( ADC10/PCINT18 )	Analog pin 10
88	PK1 ( ADC9/PCINT17 )	Analog pin 9
89	PK0 ( ADC8/PCINT16 )	Analog pin 8
90	PF7 ( ADC7 )	Analog pin 7
91	PF6 ( ADC6 )	Analog pin 6
92	PF5 ( ADC5/TMS )	Analog pin 5
93	PF4 ( ADC4/TMK )	Analog pin 4
94	PF3 ( ADC3 )	Analog pin 3
95	PF2 ( ADC2 )	Analog pin 2
96	PF1 ( ADC1 )	Analog pin 1
97	PF0 ( ADC0 )	Analog pin 0
98	AREF	Analog Reference
99	GND	GND
100	AVCC	VCC