This is second tutorial on LPC1768 where 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.

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.

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

Switch and LED bb.jpg


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.

Example 3

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.

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.


Download the complete project folder from the below link:

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