Send data before raising edge of a Clock I'm trying to control a LED strip that has a custom protocol (developed above of I2C).

But in my tests i was successful figuring out how it works :

You set Clk to zero , you send a bit in the data line , then you set Clk to high. Based on the pixels number , i should send 16bits for each color (Red Green Blue).

I was able to generate a Clock signal at 8MHz with this code : 

const byte Clock = 9;
const byte Data = 10;

void setup ()
{
 pinMode (Clock, OUTPUT);
 pinMode (Data, OUTPUT); 
 digitalWrite(Data, HIGH);
 TCCR1A = bit (COM1A0);
 TCCR1B = bit (WGM12) | bit (CS10);
 OCR1A =  0;    
 } 

 void loop ()
 {
 ...
 }  


My questions :
How could i send data at that specific time when the clock is at zero ?

Note that using digitalWrite() function was not working due to the frequency limitation of that function.

Thanks for any helpful information.
It sounds like you have some misconceptions.

In order to work with clocked signals like in SPI, you set your data line(s) to the desired value, and then raise the clock signal from low to high. The receiving device detects the low to high transition and reads the state of the data lines.

If you did it in the other order (switch the clock signal from low to high, then set the data pin(s).) then the receiver would detect the clock rising edge and try to read the data value before it was set correctly.

With a clock line like in your setup, the communication doesn't rely on fixed timing. The clock line tells the receiver when the data is available, and you can use whatever clock timing you want (up to the max speed supported by the hardware.)