b9823103_ammer_for_ARM_and_Cortex_cores__Description
[Pin] 1 [Signal] VTref [Type] Input [Description] 
This is the target reference voltage. It is used to check if the target has power, to create the logic-level reference for the input comparators and to control the output logic levels to the target. It is normally fed from Vdd of the target board and must not have a series resistor.
SEGGER | Flasher ARM | Flash Programmer for ARM and Cortex cores
Description