PD0 and PD1 as digital output and serial programmin interface

Projects General Guidance
1

Its possible to use PD0 and PD1 (RX and TX) on board without anything like example on picture, and have one of these pins as digital output? With choose to normal program running with control these pin and uploading new software?

2

Yes it is possible but not recommended, as these pins are also used by Serial and Serial.print() is often used for debugging.

3

How i can say to arduino - now run your program and use PD0 and PD1 and now is programming time?

4

You mean something like this?

pseudo code (will not compile) of an meaningless program using pin 0 and pin 1 as input/output

#define PIN_P0 0
#define PIN_P1 1

void setup()
{
  pinMode(PIN_P0, INPUT);
  pinMode(PIN_P1, OUTPUT);
}

void loop()
{
   digitalWrite(PIN_P1, HIGH);
   int x = digitalRead(PIN_P0, LOW);
}

Compile and uupload it and it will run (after you modified the bugs and added some sense to the code above :wink:

5

Telimektar:
How i can say to arduino - now run your program and use PD0 and PD1 and now is programming time?

Programming time is only available for a few moments after reset when using the normal bootloader. When your sketch is running, programming time is over. When you decide to re-program the device, the Arduino IDE automatically resets the device allowing it to enter programming time. If it is not programmed within the set amount of time, programming time is ended and your sketch starts. So you would also want to hook up the reset pin to allow for this.

6

Thanks robtillaart for example to use these pins as digital pins and Jeff K for nice explanation how this works. So after i hook up RX and TX wire and RST from ISP to reset on my board?