// Display on SSD
// connected at PORTA

// Table of values, or look up table (LUT) with the BCD codes
// for every digit from 0 to 9. Every bit corresponds to a LED,
// 1 means the LED is lit and 0 means it is off.

const unsigned char ssdlut[] = {
  0b00111111, 0b00000110,
  0b01011011, 0b01001111, 0b01100110, 0b01101101, 0b01111101,
  0b00000111, 0b01111111, 0b01101111
};
// The size of the lut
const int lutsize = 10;

int cpos = 0; //current position
int cdigit = 0; // first digit of the two
unsigned char outValue = 0;

void setup() {
  // Set port A as output
  DDRA = 0b11111111;

}

void loop() {
  
  outValue = cdigit > 0 ? 0x80 : 0;
  // which cathode are we choosing ? (00000000 sau 10000000)
  // the cathode is wired to bit7 from port A, through this
  //operation we are setting bit 7 on
  //logical 1 or
  //0, alternatively, the following bits will be attached
  //through a logical OR operation in the following line of code:
PORTA = (ssdlut[cpos] | outValue); // we make an OR
//between the value of the LUT
// and the selected cathode
cpos++; // we increment the current position
if (cpos>=lutsize) { // if we reached the final position
cpos = 0; // we come back at 0
cdigit^=1; // if the previus digit was 0 we make it a
//1 and vice versa
}
// wait 0.5 sec
delay(1000);
}