6.3 Analog Reference Voltages

The A/D converter of the AVR device needs a reference voltage to set its converting range. STK600 can supply two of these voltages; AREF0 and AREF1.

For all tinyAVR and megaAVR devices, only the AREF0 is connected through the routing card. For AVR XMEGA devices, AREF0 is connected to AREFA, and AREF1 is connected to AREFB.

For AVR XMEGA devices, the AREF pins are also general purpose I/O pins. Hence, to use the pins as GPIO, the AREF jumpers must be removed.

Note: For routing card “STK600-RC100X-13” revision A and revision B, the AREF1 is connected to PA1. These cards are marked “A0607.3.1213.A” and “A0607.3.1213.B”.

If the AREF0/AREF1 jumpers are mounted, the on-board Analog Reference Voltage sources are connected to the target AREF pins of the AVR device. The on-board Analog Reference Voltages can be adjusted from the PC software in the range 0 to 5.5V, but not above VTARGET. The resolution and accuracy is 10 mV.

The AREF0 and AREF1 generated voltages can also be connected to the analog comparator.

The target AREF signals of the AVR device are accessible on the AUX header. The figure below shows the connection of the AREF signals, the target section, and the AREF sources.