Atmega 8bit port read and write

first thing first

Arduino ports are arrange like so

PORTD = digital pins 0 through 7

PORTB = digital 8 through 13, you cant use the last two as there on the crystal

PORTC = analog 0 through 5 if your using them as digital pins pins 6 and 7 are not available on the UNO

You need to avoid normally digital pins 0 and 1 if you want to do USB serial to your computer (AKA Serial.Print(xxxx) type instructions)

so to read from a port all in one go you can do stuff like this

byte PortDataD = PORTD;

or

int myPortData = PORTD; //dont forget only the lower 8 bits are valid and you should ignore bits 0 and 1 as there the serial port

you can also write to a port like this

PORTD = B10101000; // sets digital pins 7,5,3 HIGH

but you need to remember your writing 0 to bits 0 and 1 and this could mess up any attempts to use the serial port, you may be better doing this

PORTD != B01010100; // this will set only the pins you want and leave the rest alone at their current value (0 or 1), be careful setting an input pin though as you may turn on or off the pullup resistor

you can get all the instruction on this and also setting up the ports for input and output here http://www.arduino.cc/en/Reference/PortManipulation

going this route can save masses of flash memory and increase speed almost a magnitude but you have to be more careful of what you do as your no longer protected by the "Wiring abstraction" of the hardware

Definitely a good place to go once you have mastered wiring and or running out of space in flash but still only need an ATMEGA328 CPU.

Hope this helps

Peter

I have two more questions;

I am revisiting this method of inputing data into a Arduino from a keyboard. I want to input 4 bits at a time via a port and save the data until I have 3 bytes.

I will then send this data stream via a serial port.

You have helped me understand the port addressing but I now can't seem to read data on a port.

I can write data to the port. I can then read that data and send it to Serial.print(). as in the sketch below.

However when I connect 4 switches to the PORTD (pins 2,3,4,5), I cannot read them.

Yet when I use the procedure in Arduino example "button" I can read one of the the pin states.

What am I doing wrong?

This is the basic sketch I am using for testing.

void setup()
{
Serial.begin(9600);
DDRA = B11110000;   // allows data to be read (If I am correct in my thinking)
}
void loop()
{
Serial.print(PORTA, HEX) ; // prints to monitor
PORTA = 0xF0;   //sets PORTA to HEX F0)
Serial.print(" - ");
Serial.println(PORTA,HEX);  // prints to monitor
//delay(1);
PORTA= 0xEF;  //changes data on PORTA 
//delay(1);
}

2nd question:how do I change this post to a question so I can give credit to you guys.. You are really helpful.

Thanks

Bill

I have two more questions;

I am revisiting this method of inputing data into a Arduino from a keyboard. I want to input 4 bits at a time via a port and save the data until I have 3 bytes.

I will then send this data stream via a serial port.

You have helped me understand the port addressing but I now can't seem to read data on a port.

I can write data to the port. I can then read that data and send it to Serial.print(). as in the sketch below.

However when I connect 4 switches to the PORTD (pins 2,3,4,5), I cannot read them.

Yet when I use the procedure in Arduino example "button" I can read one of the the pin states.

What am I doing wrong?

This is the basic sketch I am using for testing.

void setup()
{
Serial.begin(9600);
DDRA = B11110000;   // allows data to be read (If I am correct in my thinking)
}
void loop()
{
Serial.print(PORTA, HEX) ; // prints to monitor
PORTA = 0xF0;   //sets PORTA to HEX F0)
Serial.print(" - ");
Serial.println(PORTA,HEX);  // prints to monitor
//delay(1);
PORTA= 0xEF;  //changes data on PORTA 
//delay(1);
}

2nd question:how do I change this post to a question so I can give credit to you guys.. You are really helpful.

Thanks

Bill