1. In the digital circuit, the power supply symbol

VCC: C=circuit, which means the circuit, that is, the voltage connected to the circuit;

VDD: D=Device, which means the device, that is, the working voltage of the device;

VSS: S=Series, which means common connection, usually refers to the voltage of the common ground terminal of the circuit.

In summary, VCC is connected to the power supply of the circuit (±), VSS is connected to the ground of the circuit, and VDD is connected to the power supply pin (±) of the device.

2. Description of each pin of the power supply in STM32

VDDA: A=Analog, which means analog, so it means the working voltage of analog device;

VSSA: Represents the common ground of analog devices.

VBAT: Supply power to the backup area and maintain the preservation of some data including RTC/BKP registers.

In the 100-pin package:

VREF-: A/D reference. When needed, it must be bound to VSSA (makes the reference of all analog devices relative to VSSA).

VREF+: You can connect a separate external reference voltage to VREF+, the range is 2.0V~VDDA, and it must not exceed VDDA, otherwise it will exceed the maximum supply voltage of the analog device.

64 and fewer pins:

VREF- and VREF+ are not available. They are internally connected to an ADC voltage supply source (VDDA) and ground (VSSA). At this time, the reference voltage is the working voltage of AD.