Port Configuration of C8051F020

C8051F020 introduces the concept of cross switch, that is, the pins of the microcontroller can only be configured when the cross switch is enabled. Therefore, during initialization, the cross switch must be enabled first. The official configuration tool Config2 is very convenient and recommended for everyone to use. The pin has a weak pull-up inside (the pin is connected to VDD with a resistive connection of about 100KΩ), so the pin can output 0 and 1 if the weak pull-up is not disabled. After the weak pull-up is disabled, the pin output can be configured as push-pull and open-drain. Push-pull and weak pull-up can both output 0 and 1, but the driving capability is large, and the push-pull mode is low resistance. In this way, it can be ensured that the voltage on the port line is not divided or a very small voltage (negligible) is divided, and the output is guaranteed to be the same high level as the power supply. Push-pull is suitable for output but not for input, because if a high level is added to the push-pull (low resistance), I=U/R, I will be very large, which will cause the port to burn out. For many models of C8051F, the method of setting the I/O port to push-pull mode is: PnMDOUT=0xff, Pn=0x00, which sets the I/O port to push-pull and outputs a low level (which can reduce power consumption). If the drain is open, it can only output 0. If you need to output 1, you need to connect an external pull-up resistor. The output mode of the pin is determined by the corresponding bit in the PnMDOUT register. A certain position 1 indicates push-pull, and 0 indicates open drain (default state).

The port pins of port 1 can be used as analog inputs of the ADC1 analog multiplexer by setting the output mode to open drain and writing 1 to the corresponding bit in the port data register. The port pins can be configured as analog inputs by writing 0 to the corresponding bit in the P1MDIN register. By default, the port pins are in digital input mode.

Ports 0-3 are both bit-addressable and byte-addressable, and all port pins of ports 4-7 are only byte-addressable.