where are the 14 SAMD21 ADC pins?

Development Boards
1

I bought the Redboard Turbo board and have it set up and working under the Arduino IDE.

The sales page indicates that it has 14 ADC Channels at 12-bit Resolution. Pin A8 is not defined - it “looks” like the board only has the usual 6 ADC. Are some of the other pins also usable for ADC? I am moving from the Mega2560.

Second (unrelated) question - does the I2C arduino shield work on this board?

2

While the SAM21G as used on the Redboard DOES have the capability of 14 ADC pins, only 6 are defined in the library and usable. The other pins as used for other purposes :

     SAMD21G	     REDBOARD	INTERNAL
-------------------
PIN	PORT	ADC		
3	PA02	AIN0	A0	
4	PA03	AIN1	AREF	
7	PB08	AIN2	A1	
8	PB09	AIN3	A2	
9	PA04	AIN4	A3	
10	PA05	AIN5	A4	
11	PA06	AIN6	D8	
12	PA07	AIN7	D9	
13	PA08	AIN16	D4	
14	PA09	AIN17	D3	
15	PA10	AIN18	D1/TX0	
16	PA11	AIN19	DO/TXI	
47	PB02	AIN10	A5	
48	PB03	AIN11		FLASH_MISO

If you want to make use of some of the others the library (especially the variant.cpp and variant.h) needs to be adjusted