STM8S003F3 Interfacing with WS2811, external crystal required ?

[Vindhyachal.takniki]

1. I need to interface STM8S003F3 with WS2811. I want to know if external crystal is required for it or not, as WS2811 has very tight timings. I prefer to generate timing through NOP's for delay using inline functions
2. As STM8S003F3, Accuracy of Internal oscillator = +-5% over all temperature ranges.
3. WS2811 specifies:
   a) T0H = 0.5?s ±150ns
   b) T1H = 1.2?s ±150ns
   c) T0L = 2.0?s ±150ns
   d) T1L = 1.3?s ±150ns
   e) RES = Above 50?s
   
4. With 16Mhz crystal, time for NOP is 1/16Mhz = 0.0625us
   With on left end of accuracy -5%, time for NOP is 1/(16*.95) = 65.79ns
   With on right end of accuracy +5%, time for NOP is 1/(16*1.05) = 59.52ns

5. Are below calculations for NOP's are ok? I think internal oscillator can also be used.
   
6. a) T0H = 0.5?s ±150ns
      variation allowed around 0.5us is +-150ns i.e = 0.35us to 0.65us
     
      NOP's in T0H = 0.5?s / 0.0625us = 8
      Taking 8 NOP will generate = 0.5us
      variation with +5% accuracy = 8 * 59.52ns = 0.476us
      variation with -5% accuracy = 8 * 65.79ns = 0.526us
     
      So well within specs here
     
   b) T1H = 1.2?s ±150ns
      variation allowed around 1.2us is +-150ns i.e = 1.05us to 1.35us
     
      NOP's in T1H = 1.2?s / 0.0625us = 19.2
      Taking 19 NOP will generate = 1.1875us
      variation with +5% accuracy = 19 * 59.52ns = 1.131us
      variation with -5% accuracy = 19 * 65.79ns = 1.25us

      So well within specs here   
     
   c) T0L = 2.0?s ±150ns
      variation allowed around 2.0us is +-150ns i.e = 1.85us to 2.15us
   
      NOP's in T0L = 2.0?s / 0.0625us = 32
      Taking 32 NOP will generate = 2.0?s
      variation with +5% accuracy = 32 * 59.52ns = 1.905us
      variation with -5% accuracy = 32 * 65.79ns = 2.105us

      So well within specs here     

   d) T1L = 1.3?s ±150ns
      variation allowed around 1.3us is +-150ns i.e = 1.15us to 1.45us
   
      NOP's in T1L = 1.3?s / 0.0625us = 20.8
      Taking 21 NOP will generate = 1.3125?s
      variation with +5% accuracy = 21 * 59.52ns = 1.25us
      variation with -5% accuracy = 21 * 65.79ns = 1.382us

      So well within specs here   

   e) RES = Above 50?s
      So number of NOP's should be so that,
      at minimum clock time it should have at-least 50us
      i.e 50us / 59.52ns = 840 NOP'should
     
      Time for 840 NOP's at Min time 59.52ns = 840 * 59.52ns = 50us
      Time for 840 NOP's at nom time 62.5ns = 840 * 62.5ns = 52.5us
      Time for 840 NOP's at max time 65.79ns = 840 * 65.79ns = 55.263us
     

[edavid]

1. I need to interface STM8S003F3 with WS2811. I want to know if external crystal is required for it or not, as WS2811 has very tight timings.     

It doesn't have tight timings, just a confusing datasheet:

https://wp.josh.com/2014/05/13/ws2812-neopixels-are-not-so-finicky-once-you-get-to-know-them/