Teensyduino 3.1 ADC external reference

[dlchambers]

I'm using a Teensy 3.1 in Arduino mode.

In core_pins.h for Teensy 3 there are these defs:

#define DEFAULT         0
#define INTERNAL        2
#define INTERNAL1V2     2
#define INTERNAL1V1     2
#define EXTERNAL        0

which are the possible arg values for analogReference().

But DEFAULT and EXTERNAL are both zero... how does one tell the Teensy 3.1 to use AREF?

 

[mxxx]

But DEFAULT and EXTERNAL are both zero... how does one tell the Teensy 3.1 to use AREF?

AREF/VREFH is tied to VDDA = 3v3, so that's what it defaults to. technically then, DEFAULT uses a/the external reference; there's no difference. you can override that by using a external (shunt) voltage reference (< 3v3). take a look at the schematic for details. alternatively, analogReference(INTERNAL) will select the internal reference.