Objective
This is first example on LPC1768 where we start with blinking the LEDs. In this tutorials we are going to discuss how to configure the LPC1768 ports for GPIO and then to use to send a low/high signal on it. Lets start blinking with LEDs and then generate the different patterns using the available LEDs.
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
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 and 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 |
|---|---|
| 00 | Primary (default) function, typically GPIO port |
| 01 | First alternate function |
| 10 | Second alternate function |
| 11 | Third alternate function |
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 | FIOCLR |
|---|---|---|
| 0 | No Effect | No Effect |
| 1 | Sets High on Pin | Sets Low 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 |
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:Although it is recommended to configure the PORT direction and pin function before using it.
| Values | FIOPIN |
|---|---|
| 0 | Sets Low on Pin |
| 1 | Sets High on Pin |
Schematic
Example1
Program to demonstrate the LED blinking.
Here the first the PORT2 pins are configured as Output using the FIODIR register.
LEDs are turned ON by sending a high pulse using FIOSET register.
After some time the LEDs are turned OFF by sending the low pulse using FIOCLR register.
#include <lpc17xx.h> #include "delay.h" //User defined library which contains the delay routines /* start the main program */ void main() { SystemInit(); //Clock and PLL configuration LPC_GPIO2->FIODIR = 0xffffffff; //Configure the PORT pins as OUTPUT; while(1) { /* Turn ON all the leds and wait for one second */ LPC_GPIO2->FIOSET = 0xffffffff; // Make all the Port pins as high DELAY_sec(1); /* Turn OFF all the LEDs and wait for one second */ LPC_GPIO2->FIOCLR = 0xffffffff; // Make all the Port pins as low DELAY_sec(1); } }
Example2
This is second approach in which FIOPIN register is used for both setting and clearing the PORT pins.
Writing Logic 1 will set the PORT pin and writing 0 will Clear the particular PORT bit.
#include <lpc17xx.h> #include "delay.h" //User defined library which contains the delay routines /* start the main program */ void main() { SystemInit(); //Clock and PLL configuration LPC_GPIO2->FIODIR = 0xffffffff; //Configure the PORT pins as OUTPUT; while(1) { /* Turn ON all the LEDs and wait for one second */ LPC_GPIO2->FIOPIN = 0xffffffff; // Make all the Port pins as high DELAY_sec(1); /* Turn OFF all the LEDs and wait for one second */ LPC_GPIO2->FIOPIN = 0x00000000; // Make all the Port pins as low DELAY_sec(1); } }