LPC17xx GPIO basic

Depend on LPC17xx version the pinouts may be different. I am using 100-pin LPC1768 as an example.
Reference document: LPC17xx User manual
Require #include header lpc17xx.h
Pins on LPC1768 are divided into 5 groups (PORT) starting from 0 to 4.
Pin naming convention: P0.0 (group 0, pin 0) or (Port 0, Pin 0)
Note: if I refer to a page number, that page number is from LPC17xx User manual
Each pin has 4 operating modes: GPIO(default), 1st alternate function, 2nd alternate function, 3rd alternate function.
All GPIO pins are powered automatically so we do not need to turn on the pin power supply.

1. Pin function setting
The register LPC_PINCON control operating mode of these pins. LPC_PINCON->PINSEL0[1:0] control PIN 0.0 operating mode (page 106/835)
...
LPC_PINCON->PINSEL0[31:30] control PIN 0.15 operating mode
LPC_PINCON->PINSEL1[1:0] control PIN 0.16 operating mode
...
LPC_PINCON->PINSEL1[29:28] control PIN 0.30 operating mode
LPC_PINCON->PINSEL2[1:0] control PIN 1.0 operating mode
...
LPC_PINCON->PINSEL2[31:30] control PIN 1.15 operating mode
LPC_PINCON->PINSEL3[1:0] control PIN 1.16 operating mode
...
LPC_PINCON->PINSEL3[31:30] control PIN 1.31 operating mode
...
LPC_PINCON->PINSEL9[25:24] control PIN 4.28 operating mode
LPC_PINCON->PINSEL9[27:26] control PIN 4.29 operating mode

Note: Some register bits are reserved and are not used to control a pin. For example,
LPC_PINCON->PINSEL9[23:0] are reserved
LPC_PINCON->PINSEL9[31:28] are reserved

Bit Values Function
00 GPIO function
01 1st alternate function
10 2nd alternate function
11 3rd alternate function

Example:
To set pin 0.3 as GPIO (set corresponding bit to 00)
LPC_PINCON->PINSEL0 &=~((1 <<7)|(1<<6));

To set pin 0.3 as ADC channel 0.6 (2nd alternate function, set corresponding bit to 10)
LPC_PINCON->PINSEL0 |=((1 <<7)|(0<<6)); // you may omit (0<<6)

2. Pin direction setting
Register LPC_GPIOn->FIODIR[31:0] control the pin input/output where n is the pin group (0-4)
To set a pin as output, set the corresponding bit to 1. To set a pin as input, set the corresponding bit to 0. By default, all pins are set as input (all bits are 0).

Example:
To set pin 0.3 as output
LPC_GPIO0->FIODIR |= (1<<3);

3. A pin is set as output
Pin digital high/low setting
LPC_GPIOn->FIOSET is used to turn a pin to HIGH (page 122/835)
Register LPC_GPIOn->FIOCLR is used to turn a pin to LOW
To turn a pin to digital 1 (high), set the corresponding bit of LPC_GPIOn->FIOSET to 1. To turn a pin to digital 0 (low), set the corresponding bit of LPC_GPIOn->FIOCLR to 1.

Example:
Turn pin 0.3 to high
LPC_GPIO0->FIOSET |= (1<<3);
If we set LPC_GPIOn->FIOSET bit to 0, there is no effect
Turn pin 0.3 to low
LPC_GPIO0->FIOCLR |= (1<<3);
If we set LPC_GPIOn->FIOCLR bit to 0, there is no effect

4. A pin is set to input
a. Read a pin value
Register LPC_GPIOn->FIOPIN stores the current pin state. (page 125/835)
The corresponding bit is 1 indicates that the pin is driven high

Example:
To read current pin 0.3 state
value = ((LPC_GPIO0->FIOPIN & (1 <<3))>> 3);

Note:
Write a 1/0 to a corresponding bit in LPC_GPIOn->FIOPIN can change the output of the pin to 1/0 but it is not recommended. We should use LPC_GPIOn->FIOSET and LPC_GPIOn->FIOCLR instead.

b. Pin internal pull up setting
Register LPC_PINCON->PINMODEn is used to set up a pin internal pull up
LPC_PINCON->PINMODE0[1:0] control P0.0 internal pull up
...
LPC_PINCON->PINMODE0[31:30] control P0.15 internal pull up

Please see LPC_PINCON->PINSELn for the full list or page 110/835

Bit values Pin mode
00 on-chip pull-up resistor enabled
01 repeater mode,see page 103/835
10 tri-state mode, neither pull-up nor pull-down resistor enabled
11 on-chip pull-down resistor enabled

Example
By default all pins which are set as input has internal pull-up on (00)
To disable internal pull-up on pin 0.3
LPC_PINCON->PINSEL0 |= (1 << 7);

5. Using GPIO interrupt, only pin group 0 and 2 are used with pin interrupt
a. Falling edge interrupt
Register LPC_GPIOINT->IOxIntEnF is used to enable falling edge detected interrupt, in which x is the group number, either 0 or 2. To turn on falling edge interrupt of a pin, set the corresponding pin to 1.

Example

To enable pin 0.3 falling edge interrupt
LPC_GPIOINT->IO0IntEnF |= (1 << 3);

b. Raising edge interrupt
Register LPC_GPIOINT->IOxIntEnR is used to enable raising edge detected interrupt, in which x is the group number. To turn on raising edge interrupt of a pin, set the corresponding pin to 1.

Example

To enable pin 0.3 and 0.5 raising edge interrupt
LPC_GPIOINT->IO0IntEnR |= ((1 << 3)| (1 << 5));


c. All GPIO interrupts are connected to to EINT3 interrupt source. You need to turn EINT3_IRQn on in order to use GPIO interrupt.
NVIC_EnableIRQ(EINT3_IRQn);

d. Interrupt handler subroutine
Add this subroutine to your code. Every time the GPIO interrupts are fired (regardless of which pin), this subroutine is called.
void EINT3_IRQHandler (void)
{

}

Register LPC_GPIOINT->IOxIntStatF[31:0] has the status of which pin falling edge interrupt was fired.
Register LPC_GPIOINT->IOxIntStatR[31:0] has the status of which pin raising edge interrupt was fired.
Register LPC_GPIOINT->IOxIntClr[31:0] is used to clear the status of a pin interrupt. To clear the status bit, write 1 to the corresponding bit.

Example
To check if pin 0.3 interrupt was fired or pin 0.5 interrupt was fired
void EINT3_IRQHandler (void)
{
  if ((LPC_GPIOINT->IO0IntStatR & (1 << 3)) == (1 << 3))
  {
  //raising edge interrupt on pin 0.3 was fired
  LPC_GPIOINT->IO0IntClr |= (1 << 3); // clear the status
  //do your task
 
  return;
  }
 
  if ((LPC_GPIOINT->IO0IntStatR & (1 << 5)) == (1 << 5))
  {
  //raising edge interrupt on pin 0.5 was fired
  LPC_GPIOINT->IO0IntClr |= (1 << 5); // clear the status
  //do your task
 
  return;
  }
}