On Fri, 15 Aug 2014 13:11:53 -0400, you wrote:

>Hi all,
>
>As I've alluded to in a few other posts, I'm working on controlling
>the WS2812 LEDs. I am interested in them because they are an RGB LED
>with built in control electronics. Adafruit sells them as NeoPixels.
>They rely on a serial data stream to load their internal PWM
>registers. I think they could be extremely useful as indicator LEDs as
>they only require 1 port pin, but can be any colour I choose. Plus,
>they are chainable, so adding more LEDs doesn't require any more port
>pins.
>
>I'm using this as an intro to programming in C. At the moment I'm
>using a PIC18f25k22 running at 64MHz (16MHz x4PLL). I'm using the MSSP
>in SPI mode to control the LEDs, using some clever ideas I picked up
>here: https://www.insomnialighting.com/products/rgbsmdws2811.html .
>The super quick summary is that we're ignoring the clock line, and
>using two different 8 bit numbers to approximate the timing that the
>LED is expecting when squirted out the SDO line. It's pretty clever,
>and also frees us from having to sit in some tight timing loops and
>toggle the line manually. It does lead to a bit of confusion though as
>each byte that we're transmitting out of the MSSP is actually one bit
>to the LEDs.


if you can arrange the right bit rate, you can get one WS2812 bit per 3 SPI=
 bits.
Using a lookup table can reduce the amount of bit-twiddling if necessary.
Much more efficient on a 16 or 32 bit SPI port but should be doable on an 8=
-bit one if you can get a
400ns bit time- not familiar with the PIC18 SPIs but I've done it on a PIC3=
2


--=20
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