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
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.
Schematic
Example1
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 /* 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); } } }
Example2
This is the alternate method using the stdutils macros.
#include <lpc17xx.h> #include "delay.h" //User defined library which contains the delay routines #include "stdutils.h" #define SwitchPinNumber 11 #define LedPinNumber 0 /* start the main program */ void main() { uint32_t switchStatus; SystemInit(); //Clock and PLL configuration /* Configure the LED pin as output and SwitchPin as input */. LPC_GPIO2->FIODIR = ((1<<LedPinNumber) | (0<<SwitchPinNumber)); while(1) { /* Read the switch status */ switchStatus = util_GetBitStatus(LPC_GPIO2->FIOPIN,SwitchPinNumber); if(switchStatus == 1) //Turn ON/OFF LEDs depending on switch status { util_BitSet(LPC_GPIO2->FIOPIN,LedPinNumber); } else { util_BitClear(LPC_GPIO2->FIOPIN,LedPinNumber); } } }
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 SwitchMask 0x07 /* start the main program */ void main() { uint32_t switchStatus; SystemInit(); //Clock and PLL configuration /* Configure the LED pin as output and SwitchPin as input */. LPC_GPIO2->FIODIR = ((0<<LedPinNumber) | (SwitchMask<<SwitchPinNumber)); while(1) { /* Read the switch status*/ switchStatus = (LPC_GPIO2->FIOPIN>>SwitchPinNumber) & SwitchMask ; LPC_GPIO2->FIOPIN = (switchStatus<<LedPinNumber); //Turn ON/OFF LEDs depending on switch status } } }