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 five ports PORT0 - PORT4. 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:
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 four functions as shown below.
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 |