Re: Positional/physical addressing

On 2025-06-24, Jeroen Belleman <jeroen@nospam.please> wrote:

WS2812 LED chips do something like that. The first chip in the chain
absorbs the first three bytes and passes on all that come after, and
so on down the chain. Wait 50 us and the first chip in the chain is
ready again to intercept its three bytes.

That's not quite how they work. The whole chain is one big shift register,
(24 bits per device), with 1's and zero's being shifted along as broad
or narrow pulses. When the pulses stop for a while*, the 24 bits sitting
in the "shift register" are latched into the "DAC register" and the
colour changes.

I think I saw that there was some variant of the WS2812 that went into
a bypass mode on failure, to avoid breaking all that follow. Exactly what
counted as failure wasn't clear.

* An intersting / irritating bug had the firmware not waiting long enough
(= at all) between sending updates, so although the string was buisily
clocking data through it, nothing was happening on the lights. Getting the
bit count wrong can produce some pretty patterns, if you like migraines.


--
Ian

"Tamahome!!!" - "Miaka!!!"