STM32 has pins that can withstand 5V voltage, those marked with (FT) can directly withstand 5V, the 5V you used in 1602 is the power supply for it, you can reserve the position of 5V pull-up resistor, GPIO directly connects D0~D7, I think the logic of CMOS components 3.3V and 5V should not be a problem. And if that doesn't work you can plug in a 10K or so pull-up resistor to 5V and those pins are used to withstand 5V anyway. So it won't burn STM32. The positive and negative of the backlight generally depends on the document mark, A is, K is -; Some of them are marked on the pins. However, for safety reasons, a resistance of about 100 ohm should be connected in series to limit the current. As for the power bias, the chip is also provided internally, through the 10K potentiometer, one end is connected to GND, one end is connected to VOUT, and the display contrast can be adjusted indirectly to VO.