IO expansion headers

There are four available IO expansion headers on the kit. Because of the low pin count on the device, the IO expansion header pins are shared with onboard functionality. If “clean” expansion ports are needed, there are available cut-straps to remove onboard functionality. Following tables show what is shared on the respective header pins:

Table 1. MEGA-1284P Xplained IO expansion header – J1
Pin J1 Atmel ATmega1284P pin Shared with onboard functionality
1 TWI SDA PC1 Header J4, Boardcontroller
2 TWI SCL PC0 Header J4, Boardcontroller
3 USART RXD0 PD0 Header J4
4 USART TXD0 PD1 Header J4
5 SPI SS1 PB4 Boardcontroller
6 SPI MOSI1 PB5 Header J4, Dataflash, Boardcontroller
7 SPI MISO1 PB6 Header J4, Dataflash, Boardcontroller
8 SPI SCK1 PB7 Header J4, Dataflash, Boardcontroller
9 GND - -
10 VCC_P3V3 - -
Table 2. MEGA-1284P Xplained IO expansion header – J2
Pin J2 Atmel ATmega1284P pin Shared with onboard functionality
1 ADC02 PA0 Possible to connect to AREF
2 ADC1 PA1  
3 ADC2 PA2  
4 ADC3 PA3  
5 ADC4 PA4  
6 ADC53 PA5 Filter output
7 ADC63 PA6 Light sensor
8 ADC73 PA7 NTC sensor
9 GND    
10 VCC_ANA_P3V3    
Table 3. MEGA-1284P Xplained IO expansion header – J3
Pin J3 Atmel ATmega1284P pin Shared with onboard functionality
1 GPIO0 PB0 SW0, LED0
2 GPIO1 PB1 SW1, LED2
3 GPIO2 PB2 SW2, LED3
4 GPIO3 PB3 LED1
5 GPIO4 PD4 J4(SPI SS1), Dataflash (SPI SS1)
6 GPIO54 PD5 Filter input
7 GPIO6 PC4 JTAG(TDO)
8 GPIO7 PC5 JTAG(TDI)
9 GND    
10 VCC_P5V05    
Table 4. MEGA-1284P Xplained IO expansion header – J4
Pin J4 Atmel ATmega1284P pin Shared with onboard functionality
1 TWI SDA PC1 Header J1, Boardcontroller
2 TWI SCL PC0 Header J1, Boardcontroller
3 USART RXD1 PD2 Boardcontroller
4 USART TXD1 PD3 Boardcontroller
5 SPI SS1 PD4 Header J3(GPIO4), Dataflash
6 SPI MOSI6 PB5

Header J1, Dataflash, Boardcontroller

7 SPI MISO6 PB6 Header J1, Dataflash, Boardcontroller
8 SPI SCK6 PB7 Header J1, Dataflash, Boardcontroller
9 GND    
10 VCC_P3V3    
1 These signals can be disconnected from the boardcontroller by cutting the cut-straps marked SPI on the bottom side of the board
2 REF with 100nF capacitor to GND can be connected to ADC0 by shorting two pads marked EXTERNAL AREF on the bottom side of the board
3 These signals can be disconnected from the sensor/filter output by cutting the cut-straps marked SENSORS & FILTER on the bottom side of the board
4 This signal can be disconnected from the filter input by cutting the cut-strap marked FILTER INPUT in the SENSORS & FILTER section at the bottom side of the board
5 Pin 10 of header J3 is connected to the USB voltage (VCC_P5V0)
6 These signals can be disconnected from the boardcontroller by cutting the cut-straps marked SPI on the bottom side of the board