How to send a stream of synchronized data without frame limit

Projects Programming
1

Sorry if the title is confusing.

Say I just wanna send a series of 101010101....... @ a frequency of 1MHz (synchronized by a 1MHz clock)
or something like the one in the diagram (I need at least 3 channels)

Since Serial and I2C has extra frame bits like start/end/ACK bits, it's not a good option.
I'm not sure if SPI or other libraries can do that?
Any suggestions? Thanks in advance.

data to send.png
data to send.png1025×227 25.5 KB

2

If you just want to send an unending series of 1s and 0s just use digitalWrite(). However that is a slow function so you will probably need to use port manipulation to write directly to the I/O port.

...R

3

Where is your "clock" signal coming from? I suggest using an interrupt from the clock signal to toggle the output pins.

Paul

4

Robin2:
If you just want to send an unending series of 1s and 0s just use digitalWrite(). However that is a slow function so you will probably need to use port manipulation to write directly to the I/O port.

...R

Paul_KD7HB:
Where is your "clock" signal coming from? I suggest using an interrupt from the clock signal to toggle the output pins.

Paul

Thanks for both of your ideas. So combining port manipulation and interrupt, I finally get something like this:

int flag = 0;
void setup(){
  DDRB |= B00001110;
  cli();//stop interrupts
  TCCR3A = 0;
  TCCR3B = 0;
  TCNT3 = 0;
  OCR3A = 15;
  TCCR3B |= (1 << WGM32);
  TCCR3B |= (1 << CS30);
  TIMSK3 |= (1 << OCIE3A);
  sei();//set interrupt on Timer3 @ 1MHz
}//end setup
ISR(TIMER3_COMPA_vect){

  if (flag ==0){
    PORTB = B00001110;
    flag = 1;
  }
  else if(flag ==1){
    PORTB = B00000100;
    flag = 2;
  }
  else if(flag ==2){
    PORTB = B00001110;
    flag = 3;
  }
  else if(flag ==3){
    PORTB = B00000110;
    flag = 0;
  }
}
void loop(){
}

There's still some timing issue at such high frequency, but the format is what I'm looking for.
Thanks again

5

At 1 MHz on an Arduino UNO you only have 16 instruction cycles to do everything from interrupt handling to data output. The clock interrupt every 900-something microseconds will cause a glitch in your output about every millisecond.

   PORTB = B00001110;
   PORTB = B00000100;
   PORTB = B00001110;
   PORTB = B00000110;

It looks like your bit pattern is:
PB1-> 1011101110111011
PB2-> 1111111111111111
PB3-> 1010101010101010

So PB2 is just ON all the time, PB3 just toggles, and PB1 on 3 off 1 (offset by 1)?

6

johnwasser:
At 1 MHz on an Arduino UNO you only have 16 instruction cycles to do everything from interrupt handling to data output. The clock interrupt every 900-something microseconds will cause a glitch in your output about every millisecond.

It looks like your bit pattern is:
PB1-> 1011101110111011
PB2-> 1111111111111111
PB3-> 1010101010101010

So PB2 is just ON all the time, PB3 just toggles, and PB1 on 3 off 1 (offset by 1)?

That's just a sample. Actually I want a pattern like:
PB1:0101010101010101....(clock)
PB2:1111111111111111....(enable signal)
PB3:1111111111111111xxxx....(data[0])
PB4:0000000000000011xxxx....(data[1])

Since I don't care what the data xxxx is, I can just implement the first 16 bits (to have 8 pos-edges)and let it loop itself. As you suggest, the ISR block should be done within 16 instruction cycles, how about something like:

bool odd = true;
int pos = 1;

ISR{
iif(odd==true && pos!=15){
PORTB = B00000110;
pos++;
}
else if (odd==true && pos==15){       
PORTB = B00000111;
pos++;
}
else if (odd==false && pos!=16){       
PORTB = B00001110;
pos++;
}
else{
PORTB = B00001111;
pos = 1;
}
odd = !odd;
}

I'm not sure how IDE compiles it, but it looks like the above code goes beyond 16 cycles.
Because the clock signal with a period of 2 interrupts should be 500kHz, but the actual signal I measured has a maximum of 125kHz for the interrupt @ 1MHz,500kHz,250kHz.
Any suggestions on how to minimize the code? only need one signal to change from 0 to 1 on every 8th pos-edge, others signals are always the same.