Registers - DDR , PORT , PIN

All the configurations in microcontroller is set through 8 bit (1 byte) locations in RAM (RAM is a bank of memory bytes) of the microcontroller called as Registers.

Input Output functions are set by Three Registers for each PORT.

• DDRX (DATA DIRECTION REGISTER)‐‐‐‐> Sets whether a pin is Input or Output of PORTX.

• PORTX ‐‐‐> Sets the Output Value of PORTX.

• PINX ‐‐‐‐‐> Reads the Value of PORTX.

DDR:  

First of all we need to set whether we want a pin to act as output or input. DDRX register sets this.

• To make Input set bit 0

• To make Output set bit 1

example  DDRB=11010001

(PORT‐B)

PB7   Output     1

PB6   Output     1

PB5   Input       0

PB4   Output     1

PB3   Input       0

PB2   Input       0

PB1   Input       0

PB0   Output     1

to make a whole 8 bit port as input or output:

DDRA=255   (FOR OUTPUT PORT: 255 IS USED AS IT IS 8PIN ie  8 BIT PORT{2^8})

DDRA=0       (FOR MAKING INPUT PORT)

To make an individual pin of port as input or output:

syntax    DDRA.X=0;  (INPUT)               // WHERE X IS THE PIN NO. starting from 0 to 7

             DDRA.X=1;  (OUTPUT)

example: DDRC.5=1;                //IT MAKES 5TH PIN OF PORT C AS OUTPUT PIN

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PORT:

  This register sets the value to the corresponding PORT. Now a pin can be Output or Input. So let’s discuss both the cases.

• Output Pin

If a pin is set to be output, then by setting bit 1 we make output High that is +5V and by setting bit 0 we make output Low that is 0V.

SYNTAX:

PORTX ‐‐‐‐> to set value of PORTX with a byte.

PORTX.y ‐‐> to set value of yth pin of PORTX with a bit (works only with CVAVR)

example: PORTA.4=0;                       //GIVE 0 VOLT AT OUTPUT OF PIN 4 OF PORT A

PORTB=255;                             //GIVE 5 VOLT AT OUTPUT OF ALL PINS OF PORT B

• Input Pin

If a pin is set to be input, then by setting its corresponding bit in PORTX register will make it as follows, Set bit 0 ‐‐‐> Tri‐Stated Set bit 1 ‐‐‐> Pull Up

Tristated means the input will hang (no specific value) if no input voltage is specified on that pin.

Pull Up means input will go to +5V if no input voltage is given on that pin. It is basically connecting

PIN to +5V through a 10K Ohm resistance.

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PIN register:

This register is used to read the value of a PORT. If a pin is set as input then corresponding bit on PIN register is,

• 0 for Low Input that is V < 2.5V

• 1 for High Input that is V > 2.5V (Ideally, but actually 0.8 V ‐ 2.8 V is error zone!)

SYNTAX:

• PINX ‐‐‐‐> Read complete value of PORTX as a byte.

• PINX.y ‐‐> Read yth pin of PORTX as a bit (works only with CVAVR).

example  if(PINA.1==1)

              {

             ___                      

             ___

              }

    // READ IF VALUE AT PIN 1 OF PORT A IS 1 OR NOT, IF IT IS 1 THEN IT EXECUTES INSTRUCTIONS UNDER if STATEMENT

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