LPC1768: Switch and LED

we are going to read the switches and turn ON/OFF the LEDs accordingly. LPC1768 has its GPIOs divided into five ports PORT0 - PORT4, although many of them are not physically 32bit wide. Refer the data sheet for more info.

Register Configuration

The Below registers will be used for Configuring and using the GPIOs registers for sending and receiving the Digital signals.

PINSEL: GPIO Pins Select Register

Almost all the LPC1768 pins are multiplexed to support more than 1 function. Every GPIO pin has a minimum of one function and max of four functions. The required function can be selected by configuring the PINSEL register. As there can be up to 4 functions associated with a GPIO pin, two bits for each pin are available to select the function. This implies that we need two PINSEL registers to configure a PORT pins. By this the first 16(P0.0-P0.16) pin functions of PORT0 can be selected by 32 bits of PINSELO register. The remaining 16 bits(P0.16-P0.32) are configured using 32bits of PINSEL1 register. As mentioned earlier every pin has max of four functions. Below table shows how to select the function for a particular pin using two bits of the PINSEL register.

Value	Function	Enumeration
00	Primary (default) function, typically GPIO port	PINSEL_FUNC_0
01	First alternate function	PINSEL_FUNC_1
10	Second alternate function	PINSEL_FUNC_2
11	Third alternate function	PINSEL_FUNC_3

FIODIR:Fast GPIO Direction Control Register.
This register individually controls the direction of each port pin.

Values	Direction
0	Input
1	Output

FIOSET:Fast Port Output Set Register.
This register controls the state of output pins. Writing 1s produces highs at the corresponding port pins. Writing 0s has no effect. Reading this register returns the current contents of the port output register not the physical port value.

Values	FIOSET
0	No Effect
1	Sets High on Pin

FIOCLR:Fast Port Output Clear Register.
This register controls the state of output pins. Writing 1s produces lows at the corresponding port pins. Writing 0s has no effect.

Values	FIOCLR
0	No Effect
1	Sets Low on Pin

FIOPIN:Fast Port Pin Value Register.
This register is used for both reading and writing data from/to the PORT.
Output: Writing to this register places corresponding values in all bits of the particular PORT pins.
Input: The current state of digital port pins can be read from this register, regardless of pin direction or alternate function selection (as long as pins are not configured as an input to ADC).
Note:It is recommended to configure the PORT direction and pin function before using it.

Hardware Connections

Examples

Example 1

In this program, we are going to do both INPUT and OUTPUT operation. The port pin to which switch is connected is configured as Input and the pin to which LED is connected is configured as OUTPUT. Here the switch status is read and accordingly the LED will be turned ON/OFF.

	#include <lpc17xx.h>
	#define SwitchPinNumber 11
	#define LedPinNumber 0
	/* start the main program */
	void main()
	{
	uint32_t switchStatus;
	SystemInit(); //Clock and PLL configuration
	LPC_PINCON->PINSEL2 = 0x000000; //Configure the Pins for GPIO;
	/* Configure the LED pin as output and SwitchPin as input */.
	LPC_GPIO2->FIODIR = ((1<<LedPinNumber) | (0<<SwitchPinNumber));
	while(1)
	{
	/* Turn On all the leds and wait for one second */
	switchStatus = (LPC_GPIO2->FIOPIN>>SwitchPinNumber) & 0x01 ; // Read the switch status
	if(switchStatus == 1) //Turn ON/OFF LEDs depending on switch status
	{
	LPC_GPIO2->FIOPIN = (1<<LedPinNumber);
	}
	else
	{
	LPC_GPIO2->FIOPIN = (0<<LedPinNumber);
	}
	}
	}