Tutorial 2 - Understanding General Purpose I/O of AT32UC3A using EVK1105

Introduction

AT32UC3A0 series MCU has 109 GPIO pins. Each GPIO pin can be programmed for digital input, digital output or it can be assigned to one of 3 peripheral functions, which is specific to that pin.

Example

GPIO pin 21(PA21) can be programmed to be used as general purpose digital I/O, or it can be configured for Analog input

Each GPIO line has a unique number. PA, PB, PC and PX ports do not directly correspond to the GPIO ports. To find the corresponding port and pin, the following formulas can be used:

GPIO port = floor((GPIO number) / 32), example: floor((36)/32) = 1
GPIO pin = GPIO number mod 32, example: 36 mod 32 = 4

Example: Say if LED0 is on PB27. By referring AT32UC3A0512 datasheet pg.47, we know that  GPIO number for PB27 is 59, therefore

GPIO port = floor(59/32) = 1
GPIO pin = 59 mod 32 = 27

Now lets see how the GPIO can be configured for digital out on LED1(PB28, GPIO number 60) without using ASF.

 1: #include <asf.h>
 2: 
 3: int main (void)
 4: {
 5:  
 6:  AVR32_GPIO.port[1].gpers |= 1 <<28;  //enable GPIO control
 7:  AVR32_GPIO.port[1].oders |= 1 <<28;  //enable output driver
 8:  
 9:  AVR32_GPIO.port[1].ovrc |= 1 << 28;  //clear the gpio pin
10:  
11:  while(1);
12:  
13: }

If PB28(GPIO number 60,  AT32UC3A0512 datasheet pg.47 ) i.e LED1 is to be set for digital out, we have to find GPIO port and pin for it first.

So using the formula,

GPIO port = floor(60/32) = 1

GPIO pin = 60 mod 32 = 28
We have to configure now the GPIO port 1, pin 28 for be digital out and not for peripheral function.

It is done by setting bit in gpers register. If the bit is clear, then GPIO pin will be used for peripheral function.

AVR32_GPIO.port[1].gpers |= 1 <<28;

The above line sets 28th pin on GPIO port 1. Now the pin will act as GPIO I/O

Now to set the GPIO pin 28 of port 1 as output, we have to set the 28th bit on oders(Output Driver Enable Register)

AVR32_GPIO.port[1].oders |= 1 <<28;  //enable output driver

And to set output value low, we have to set bit Output Value Register Clear(ovrc) register

AVR32_GPIO.port[1].ovrc |= 1 << 28;

Since LED is connected between vcc and the pb28, so by setting the pin low , led will turn on.

Refer pg175 of AT32UC3A datasheet for complete description of GPIO registers.