Reading an I/O pin

[pontus]

Posted on March 17, 2008 at 06:39

Reading an I/O pin

[pontus]

Posted on May 17, 2011 at 09:50

Hi,

i am just getting started on the STR912FW44x, and have a big problem. I just want to read the state of GPIO pins 7.4-7.7 (which have pushbuttons connected to them, pressed = grounding). I believe I have initialized everything correctly, but (in the unpressed state) the pins still read as low even though they are high (I have double-checked with a multimeter). If I check the GPIO DATA registers using my debugger, they too show that GPIO7 has all pins low. Can somebody give me any hints as to what is going on here?

I have the STR912F Eval board from Hitex, see:

http://www.hitex.com/products.html?con_arm_evaluation_board_str912.html~content

Plus the debugger and everything listed here:

http://www.hitex.com/con_arm_starter_kit_str9.html

My toolchain is the Hitop IDE + GCC.

my main.c:

#include ''91x_lib.h''

GPIO_InitTypeDef GPIO_InitStructure;

int main()

{

int foo;

/* GPIO Configuration -----*/

//GPIO 8 controls the LED segment display

GPIO_StructInit(&GPIO_InitStructure);

GPIO_DeInit(GPIO8);

GPIO_InitStructure.GPIO_Direction = GPIO_PinOutput;

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_All ;//0 | GPIO_Pin_1 | GPIO_Pin_2 | GPIO_Pin_3;

GPIO_InitStructure.GPIO_Type = GPIO_Type_PushPull ;

GPIO_Init (GPIO8, &GPIO_InitStructure);

//GPIO9 controls a transistor for activating the entire led display. write 0 to activate.

GPIO_StructInit(&GPIO_InitStructure);

GPIO_DeInit(GPIO9);

GPIO_InitStructure.GPIO_Direction = GPIO_PinOutput;

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_All ;//0 | GPIO_Pin_1 | GPIO_Pin_2 | GPIO_Pin_3;

GPIO_InitStructure.GPIO_Type = GPIO_Type_PushPull ;

GPIO_Init (GPIO9, &GPIO_InitStructure);

GPIO_WriteBit(GPIO9, GPIO_Pin_0, Bit_RESET);

GPIO_WriteBit(GPIO9, GPIO_Pin_1, Bit_RESET);

//GPIO7 has pushbuttons connected to 7.4-7.7. button pressed = pin low. otherwise

// high thanks to a pull-up resistor.

GPIO_StructInit(&GPIO_InitStructure);

GPIO_DeInit(GPIO7);

GPIO_InitStructure.GPIO_Direction = GPIO_PinInput;

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4 | GPIO_Pin_5 | GPIO_Pin_6 | GPIO_Pin_7;

GPIO_InitStructure.GPIO_Type = GPIO_Type_PushPull ;

GPIO_Init (GPIO7, &GPIO_InitStructure);

GPIO_WriteBit(GPIO8, GPIO_Pin_All, Bit_SET); //all led segments OFF

foo = 1; //default state is button not pressed (GPIO HIGH)

while(1)

{

//foo = (((GPIO7->DR[GPIO_Pin_5<

foo = GPIO_ReadBit(GPIO7, GPIO_Pin_5); //read pin

GPIO_WriteBit(GPIO8, GPIO_Pin_2, foo); //if pin low (button pressed), a LED segment will lit up

}

}

I would be extremely thankful for any help I can get. I have been trying to solve this problem for several days now I I just can't find the problem!

[ This message was edited by: pontus.froessander on 08-05-2008 11:16 ]

[jpeacock2]

Posted on May 17, 2011 at 09:50

The input pins need to be configured for open drain instead of push-pull.

[jpeacock2]

Posted on May 17, 2011 at 09:50

You will also need to write a '1' to the port pin before reading it back. In open drain mode there is an internal FET switch to pull the pin low. The '1' turns off that FET.

In push-pull there's an additional FET to pull the pin hi, most likely why you see a bad reading. Don't leave the pin in P-P mode as you have an output driver driving a ground when the switch is closed to ground. Lots of wasted current that way.

[pontus]

Posted on May 17, 2011 at 09:50

Thanks for your reply. I tried the following code:

//GPIO7 has pushbuttons connected to 7.4-7.7. button pressed = pin low. otherwise

// high thanks to a pull-up resistor.

GPIO_StructInit(&GPIO_InitStructure);

GPIO_DeInit(GPIO7);

GPIO_InitStructure.GPIO_Direction = GPIO_PinInput;

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4 | GPIO_Pin_5 | GPIO_Pin_6 | GPIO_Pin_7;

GPIO_InitStructure.GPIO_Type = GPIO_Type_OpenCollector ;

GPIO_Init (GPIO7, &GPIO_InitStructure);

GPIO_Write(GPIO7, 0xFF);

But it still doesn't work! I also tried writing a 1 to the port but in push-pull mode. Oh and I also tried doing it both before and after initializing the port. Argh - I am slowly going crazy :). More tips :)?