MEAM.Design : M4 : I/O Ports (GPIO)

MEAM.Design - M4 - I/O Ports (GPIO)

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There are 26 GPIO pins on the M4 board, spread across ports A, B, C, E, and F. All of the pins can be configured as push-pull or open-drain with selectable internal pull-up resistors or pull-down resistors or none, and include protection diodes to Vcc and ground (thankfully!). Each port is 16 bit wide while only a subset of those pins can be used.

On port A: 0-6, 8-10
On port B: 0-9, 14
On port C: 15 (also connected to the yellow LED)
On port D: none
On port E: 8,9
On port F: 6,7
This procedure for configuring a pin for GPIO assumes that the clock initialization and prescalers have been setup. This is taken care of in mInit() for you.

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The GPIO functions require you to input variables in order to specify both a port and a pin.

For ports, the variable GPIOx is used, where the x is replaced with the port letter (ranging from A to F).

For pins, the variable GPIO_Pin_n is used, where the n is replaced with the pin number (ranging from 0 to 15)

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To configure and use a port pin:

1) #include mGeneral.h

Note that you don't have to include the other headers such as the GPIO header (stm32f37x_gpio.h), this is all done for you in mGeneral.h

2) Initialization:

we use the function,

GPIO_Init(GPIOx, &GPIO_InitStruct);

You must declare the second variable (which is a structure of type GPIO_InitTypeDef) as follows:

GPIO_InitTypeDef GPIO_InitStruct;

The GPIO_InitStruct Structure has 5 fields to set 5 different parameters:

i) GPIO_InitStruct.GPIO_Pin

Possible values: GPIO_Pin_All, GPIO_Pin_n, where n is defined above (can be OR'ed to set multiple pins at one time)

ii) GPIO_InitStruct.GPIO_Mode

Possible values: GPIO_Mode_OUT, GPIO_Mode_IN, GPIO_Pin_AF, GPIO_Mode_AN

[output, input, alternate function, analog]

iii) GPIO_InitStruct.GPIO_Speed

Possible values: GPIO_Speed_Level_1, GPIO_Speed_Level_2, GPIO_Speed_Level_3

[where 1 is slowest, 3 is fastest]

iv) GPIO_InitStruct.GPIO_OType

Possible values: GPIO_OType_PP, GPIO_OType_OD

[push-pull output, and open-drain output, respectively]

v) GPIO_InitStruct.GPIO_PuPd

Possible values: GPIO_PuPd_NOPULL, GPIO_PuPd_UP, GPIO_PuPd_DOWN

[neither, pull up, pull down]

For example, if say you want to configure Pins PA2 and PA6 as Output-SpeedLevel2-PushPull-NoPullup pins

	GPIO_InitTypeDef GPIO_InitStruct;
	GPIO_InitStruct->GPIO_Pin  = GPIO_Pin_2 | GPIO_Pin_6;
	GPIO_InitStruct->GPIO_Mode = GPIO_Mode_OUT;
  	GPIO_InitStruct->GPIO_Speed = GPIO_Speed_Level_2;
  	GPIO_InitStruct->GPIO_OType = GPIO_OType_PP;
  	GPIO_InitStruct->GPIO_PuPd = GPIO_PuPd_NOPULL;
	GPIO_Init(GPIOA, &GPIO_InitStruct);

3) Reading:

GPIO_ReadInputData(GPIOx, GPIO_Pin_n);

This returns a 16-bit representation of input data pin n on port x.

GPIO_ReadOutputData(GPIOx);

This returns a 16-bit representation of output data pin n on port x.

4) Setting and clearing:

GPIO_SetBits(GPIOx, GPIO_Pin_n);

This sets pin n on port x.

NOTE: for port F, n can only =6

GPIO_ResetBits(GPIOx, GPIO_Pin_n);

This clears pin n on port x.

5) Writing:

GPIO_Write(GPIOx, PortVal);

This writes the value PortVal to port x, where PortVal is a 16 bit unsigned int.

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Important Notes:

The maximum current output for any of the pins should NEVER exceed 4mA.