Revision as of 13:15, 30 May 2015

Objective

This is Second example on LPC1768 where we are going to read the switchs and turn ON/OFF the LEDs accordingly.

Register Configuration

As all the LPC1768 SFRs(Special Function Registers) are defined in lpc17xx.h, this has to be included at the beginning of our project/code.

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. The Below registers will be used for Configuring and using the GPIOs registers for sending and receiving the Digital signals. A structure LPC_GPIOn(n= 0,1,2,3) contains all the registers for required for GPIO operation. Refer lpc17xx.h file for more info on the registers.

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 concludes 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.

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

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.

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.

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.

Schematic

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.

Example 2

This is the alternate method using the stdutils macros.

Example3

In this program multiple(3) switches are read and multiple LEDs are turned ON/OFF depending on the respective switch status. As shown in the schematic the LEDs are connected from P2.0 to P2.3. And the switches are connected to P2.10 to P2.12, accordingly the 3bit mask will be 0x07.

#include <lpc17xx.h>   
 
#define SwitchPinNumber 10
#define LedPinNumber    0
 
#define ThreeBitMask   0x07
 
 
/* start the main program */
void main() 
{
    uint32_t switchStatus;
    SystemInit();                    //Clock and PLL configuration 
    LPC_PINCON->PINSEL2 = 0x000000; //Configure the Pins for GPIO;
 
    /* Configure all the LED pins as output and SwitchPins as input */
    LPC_GPIO2->FIODIR = ((ThreeBitMask<<LedPinNumber) | (0<<SwitchPinNumber)); 
 
  while(1)
    {
 
     /* Read the switch status*/ 
       switchStatus = (LPC_GPIO2->FIOPIN>>SwitchPinNumber) & ThreeBitMask ;                           
       LPC_GPIO2->FIOPIN = (switchStatus<<LedPinNumber);  //Turn ON/OFF LEDs depending on switch status
    }
}

Using Explore Embedded Libraries:

In the above tutorial we just discussed how to configure the PORTS for GPIO and use them for reading/wring the pins
Once you know the GPIO configurations, you can directly use the ExploreEmbedded libraries
For that you need to include the gpio.c/gpio.h and the associated files(delay/stdutils).
The below sample code shows how to use the GPIO functions.

Refer this link for more info on GPIO libraries.

#include <lpc17xx.h>   
#include "delay.h"     //User defined library which conatins the delay routines
#include "gpio.h"
 
#define MY_LED    P2_0     // Led is connected to P2.0
#define MY_SWITCH P2_10    // Switch is connected to P2.10
 
/* start the main program */
void main() 
{
    uint8_t value;
    SystemInit();                                                 //Clock and PLL configuration
 
    GPIO_PinFunction(MY_SWITCH,PINSEL_FUNC_0); // Configure Pin for Gpio
    GPIO_PinDirection(MY_SWITCH,INPUT);          // Configure the switch pin as Input
 
    GPIO_PinFunction(MY_LED,PINSEL_FUNC_0); // Configure Pin for Gpio
    GPIO_PinDirection(MY_LED,OUTPUT);       // Configure the Led pin as OUTPUT
 
  while(1)
    {
 
       value = GPIO_PinRead(MY_SWITCH);         // Read the switch status
       GPIO_PinWrite(MY_LED,value);              // ON/OFF the led as per switch status  
    }
}

Downloads

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