STM32F100xx LQFP64 Pin Functions
Created on: 29 August 2012
When learning a new microcontroller, a good understanding of pin functions is essential. Here we look at several views of STM32F100xx microcontroller pins and functions (LQFP64).
Applies to the STM32F100RB used on the STM32 value line discovery board.
The image below will be shown throughout this article with different pins / pin functions highlighted such as port pins, power pins, dedicated pins, oscillator pins, debug pins, etc.
Port, Power and Dedicated Pins
STM32F100xx microcontrollers that are packaged in LQFP 64 pin packages have the following basic pin functions:
Port Pins
Three 16-bit ports and one 3-bit port:
- PA0 to PA15 (16 pins)
- PB0 to PB15 (16 pins)
- PC0 to PC15 (16 pins)
- PD0 to PD2 (3 pins)
Total = 51 pins
Power Pins
Ten power pins:
- 4 × VDD
- 4 × VSS
- 1 × VDDA – analog supply and reference voltage
- 1 × VSSA – analog supply and reference voltage
Total = 10 pins
Dedicated Pins
Three dedicated pins:
- VBAT – backup power for RTC, external 32kHz oscillator and backup registers.
- NRST – reset pin.
- BOOT0 – selects boot mode, boots from main Flash when 0.
Total = 3 pins
The diagram below shows the top view of a STM32F100xx microcontroller in a 64 pin LQFP. The power and dedicated pins are highlighted.
Debug and Oscillator Pins
The image below shows the oscillator pins and the JTAG / SWD pins highlighted.
The main oscillator pins are shown in brown and the 32.768kHz oscillator pins are shown in purple.
JTAG pins are shown in blue. The JTAG pins are dedicated to JTAG functionality at reset and these pins are not GPIO pins by default. The SWD (Serial Wire Debug) pins shown in olive share two of the JTAG pins.
Default Pin Functions after Reset
STM32F100xx LQFP64 microcontrollers have the default pin functions shown below after reset (shown in orange).
The pins shown in green will be port pins as shown after power-up. However, if the microcontroller is later reset, their function will depend on the contents of the Backup registers which are not reset by the main reset.
Note also that the function of PD0 (pin5) and PD1 (pin6) can be remapped by software.
I/O Pin Alternate Functions
The image below shows the alternate pin functions of STM32F100xx devices. The alternate functions are the internal peripheral device connections to the external pins.
Alternate functions shown in red can be remapped to other port pins. The port pins that they can be remapped to are not shown.
Alternate functions shown in blue are not available in low density STM32F100 devices. These are the second I²C port, the second SPI port and TIM4. TIM4 is shown in red and blue as it can be remapped and does not exist on low density devices.
