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Understanding DP1903 timing (WS2811 variant)

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Vindhyachal Takniki

Joined Nov 3, 2014
598
1. I am writing code for interfacing DP1903 with MCU. MCU is run by 16Mhz internal oscillator.
As per DP1903 datasheet;
TIH = 2us & T1L = 0.5us +-150ns
T0H = 0.5us & T0L = 2us +-150ns
Treset >= 24us

2. Data-sheet: http://www.depuw.com/Public/images/pdf/depuw/DP1903.pdf
Page 4 & 5 specify timings.

3. What is purpose of mentioning 800Khz & 400Khz speed? How does I have to account this is in code?
Data-sheet specify timings as already written in point 1, so I need to write code according to that, right?
So how does this 800Khz comes in between? What does it signify?

4. Suppose I have to send a zero & then a reset pulse at some given point.
So timing will be T0H, T0L & Treset, i.e
a. Pin high for 0.5us
b. Pin low for 2.0us
c. Pin low for 24us

Do after step b, I have to make high & then low again? As in page4, on T0L completion bit again goes to high? Or it is for representation only, I can combine step b & c & keep pin low for 24+2 = 26us?

5. Attached is my code. I saw some problem sometimes when I run the code. Code is run on full speed optimization i.e O3,
mainly problem occurs when I turn on all lights blue, The lights do not go all blue, but some whitish color appears.

6. I have 100 led connected. Also noticed if I make 24us delay, color don't appear correctly at all, with 50us there is some problem, increasing further delay don't have any effect. Why is that so?
7. For 0.5us, 8 nops are used, while for 2us, 32 nops are used.


Code: 
int main(void)
{
    LED_pin_output_low();

    while(1)
    {
        ws2811_reset_us(50);
        for(led_cnt = 0U ; led_cnt < 100U ; led_cnt++)
        {
            ws2811_rgb_write(0xff, 0x00, 0x00);
        }
        delay_sec(2);
      
        ws2811_reset_us(50);
        for(led_cnt = 0U ; led_cnt < 100U ; led_cnt++)
        {
            ws2811_rgb_write(0x00, 0xff, 0x00);
        }
        delay_sec(2);
      
        ws2811_reset_us(50);
        for(led_cnt = 0U ; led_cnt < 100U ; led_cnt++)
        {
            ws2811_rgb_write(0x00, 0x00, 0xff);
        }      
        delay_sec(2);
      
    }
      
} /* function ends here */



static void ws2811_rgb_write(uint8_t red, uint8_t green , uint8_t blue)
{
    uint8_t red_arr[8];
    uint8_t green_arr[8];
    uint8_t blue_arr[8];

    uint8_t cnt;
    uint8_t idx;

/* store the bits values of RGB in a array */  
    idx = 0x80U;
    for(cnt = 0U; cnt < 8U; cnt++)
    {
        if(red & idx)
        {
            red_arr[cnt] = 1U;
        }
        else
        {
            red_arr[cnt] = 0U;
        }

        if(green & idx)
        {
            green_arr[cnt] = 1U;
        }
        else
        {
            green_arr[cnt] = 0U;
        }
      
        if(blue & idx)
        {
            blue_arr[cnt] = 1U;
        }
        else
        {
            blue_arr[cnt] = 0U;
        }        
      
        idx = idx >> 1U;
    }
  
/* send pixels as fast as possible */
/* red pixel */  
    if(red_arr[0]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(red_arr[1]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(red_arr[2]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(red_arr[3]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(red_arr[4]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(red_arr[5]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(red_arr[6]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }    
    if(red_arr[7]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }

/* green pixel */
    if(green_arr[0]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(green_arr[1]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(green_arr[2]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(green_arr[3]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(green_arr[4]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(green_arr[5]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(green_arr[6]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }    
    if(green_arr[7]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }

/* blue pixel */
    if(blue_arr[0]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(blue_arr[1]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(blue_arr[2]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(blue_arr[3]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(blue_arr[4]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(blue_arr[5]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
    if(blue_arr[6]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }    
    if(blue_arr[7]) { ws2811_bit_set(); }  else { ws2811_bit_reset(); }
  
} /* function ends here */



static inline void ws2811_bit_set(void)
{
    LED_PIN_ON();
  
    __no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();
    __no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();
    __no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();
    __no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();
  
    LED_PIN_OFF();

    __no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();
      
}



static inline void ws2811_bit_reset(void)
{
    LED_PIN_ON();
  
    __no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();
  
    LED_PIN_OFF();

    __no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();
    __no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();
    __no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();
    __no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();__no_operation();
  
}
 
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