Specification:
Processor: STM32F103RC8T6, 32 ARM Cortex-M3 processor
Frequency: 72 MHz
64 KB Flash and 20 KB SRAM
34 digital io ports (GPIOs)
12 16-bit precision PWM port
9 12 precision analog input (ADC) port
2 SPI channel
2 I2C channel
7-channel direct memory access (DMA) (dma.h)
3 USART (serial) channel
An enhanced and three general purpose timers
Can be downloaded directly via the USB port and communications program
An external JTAG
Nested Vectored Interrupt Controller (NVIC) (including GPIOs on the external interrupt)
Support for low-power, sleep and standard mode (<500 μA)
Operating Voltage: 3.3 V
Input Voltage (recommended): 3 V - 12 V
Size: 2.02 "× 0.72"

Maple Mini has a total of 34 input / output pins, numbered from D0 to D33. Maple Mini label on the screen corresponds to the port and its adjacent. However, they have some of the default has a special purpose.
D23 is the USB port D +, D24 is the USB D-. Such as their use as GPIO, then your program must first disable the USB port. But you know, disable USB serial bootloader means that priority will not work, you will need to pass Perpetual Bootloader for the next update.
Port D32 is the Mini button port. Therefore, it is mainly used as an input port. When the key is pressed, the magnetic port will read high.
Port D33 is the Mini LED port. Therefore, its main role is as an output port. When it was written with high, LED lights will be lit