Port A and Port B ~ Port H / J have different features, and each bit in GPACON corresponds to a pin, a total of 23 pins. When a bit is set to 0, the corresponding pin is the output pin. At this point we can write 1 or 0 in GPADAT to make this pin output high or low;
When a bit is set to 1, the corresponding pin is the address line or for address control, and GPADATA is useless. Generally, GPACON is typically set to 1 to access external devices. Port B ~ Port H / J is exactly the same in register operation, and each two of GPXCON controls a pin, 00 input 01 output 10 special function 11 reserved
Differences between various modes of GPIO port
(1) GPIO_MODE_AIN simulation input
(2) GPIO_MODE_IN_FLOATING Empty Input
(3) GPIO_MODE_IPD drop-down input
(4) GPIO_MODE_IPU pull-up input
(5) GPIO_MODE_OUT_OD open drain output
(6) GPIO_MODE_OUT_PP push-pull output
(7) GPIO_MODE_AF_OD multiplexing output
(8) GPIO_MODE_AF_PP multiplex push output
1.1 In the output mode of the I / O port, there are three output speed optional (2 MHz, 10MHz and 50MHz). This speed refers to the speed of the I / O port drive circuit rather than the output signal, the speed of the output signal is The program is related (the number of output driving circuits in which multiple response speeds can be arranged inside the I / O port), and the user can select the appropriate drive circuit according to their own needs. Different output drive modules are selected by selecting speeds to achieve optimal noise control and purpose of reducing power consumption. High-frequency drive circuit, noise is also high, when high output frequencies are not required, use low frequency drive circuits, which is very beneficial to improve the EMI performance of the system. Of course, if you want to output a higher frequency signal, the lower frequency drive module is selected, which is likely to get the output signal of the distortion.
The key is that GPIO's pin speed is matched with the application (recommended more than 10 times?).
for example:
1.1.1 For serial ports, if the maximum baud rate is only 115.2k, then the pin speed of 2M GPIO is enough, and it is saved and noise.
1.1.2 For the I2C interface, if you use a 400K baud rate, if you want to leave the margin, the pin speed of 2M GPIO may be insufficient, and the 10M GPIO pin speed can be selected.
1.1.3 For the SPI interface, if the 18m or 9M baud rate is used, the pin speed of 10M GPIO is obviously not enough, and the pin speed of 50M GPIO is required.
1.2 GPIO oral is set to input, the output drive circuit and the port are disconnected, so the output speed configuration is meaningless.
1.3 After the reset period and just reset, the multiplexing function is not turned on, and the I / O port is configured to float input mode.
1.4 All ports have external interrupt capabilities. In order to use an external interrupt line, the port must be configured to input mode.
1.5 The configuration of the GPIO port has a lock function. When the GPIO port is configured, the configuration combination can be locked by the program until the next chip reset can be unlocked.
2, the difference between push-pull output and open drain output
Push-pull output: can output high, low, connect digital devices; open drain output: The output is equivalent to the collector of the triode. It is necessary to get the high-level status. Suitable for doing current type driving, its ability to absorb current is relatively strong (generally within 20 mA).
The push-pull structure typically refers to the control of two triodes being controlled by two mutual replenishment signals, always turned on when a triode is turned on.
To implement line and need OC (Open Collector) gate circuit. It is the same triode or MOSFET in two parameters, exists in the push-pull method in the circuit, each responsible for the waveform amplification task of the positive and negative half-week, when the circuit works, the two symmetrical power switch tubes only one conduction each time, Small loss and high efficiency. Output can be applied to load, or current from load extraction
When the port is configured to output:
Open drain mode: When 0 is output, N-MOS is turned on, and P-MOS is not activated, output 0.
When output 1, N-MOS high resistance, P-MOS is not activated, output 1 (require external pull-up circuit); this mode can be used as two-way IO.
Push-pull mode: When output 0, N-MOS is turned on, P-MOS high resistance, and output 0.
When 1 is output, the N-MOS high resistance, P-MOS is turned on, and output 1 (no external pull-up circuit) is required.
Simply speaking, when the leak is 0, when the GND 1 is connected, the floating push-pull is 0 when I pick up the GND 1, I will pick up VCC.
3, choose IO mode in STM32
(1) Floating input _in_floating - floating input, you can do Key recognition, RX1
(2) Belt uplift input _ipu - IO internal pull-up resistor input
(3) With drop-down input _iPD-IO internal pull-down resistor input
(4) Simulation input _ain - Apply ADC analog input, or save power under low power
(5) Open drain output _out_od --io output 0 picks up GND, IO output 1, suspended, need external pull-up resistors to implement output high. When the output is 1, the state of the IO port is highly pulled by the pull-up resistance, but since it is an open drain output mode, the IO port can be changed from an external circuit to a low or constant. You can read the IO input level change, implement the IO two-way function of C51
(6) Push-pull output _Out_pp --io output 0-connected GND, IO output 1 - connected VCC, read input values is unknown
(7) Push-pull output for multiplexing function _AF_PP - Intravencens (I2C SCL, SDA)
(8) Open drain output of multiplexing _AF_OD - Internally and external function (TX1, MOSI, MISO.SCK.SS), Technology Zone
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