ESP8266 Community Forum

There are a bunch of things that the datasheet mentions, but then remain unexplained This is a topic to list them all in one place. I'll try to keep a TOC of this topic in this here first post.

One subject per post,please. Makes it easier to read.
So here goes:

TOC:

1. Using an external Low Frequency Clock signal.

The latest specifications data sheet (EX version, http://www.esp8266.com/download/file.php?id=79) mentions using an external Low-Frequency Clock:

ESP8266_Specifications_v4.0 wrote:8.4.3 Real Time Clock IO (EXT_LFC)
If a 32.768 kHz LFC clock is available, it can be connected to EXT_LFC. If no clock is
available on this pin, the internal LFC will be used. If an EXT_LFC is available, the selection of
LFC source, internal LFC or EXT_LFC can be done by a strapping pin.

Questions:

1. What pin is EXT_LFC?
2. What pin selects between the internal and external clock?
3. What levels should the clock signal be? The usual GPIO levels? 0...1.1?
4. Is this feature new to the ESP8266EX, or is it available on the non-EX versions as well?
5. What accuracy can we expect from the internal clock?
6. What is VDD_RTC?

My geuss is that VDD_RTC is used to keep the clock running and should be at least 1.1V. Another assumption is that only an internal RTC is available (ie. I dont see those other pins broken out (in the documentation I got))

Sjaak wrote:...in the documentation I got...

The whole point of the thread is to clarify those claims in the datasheet from Espressif themselves, instead of guessing. I think we can agree that the English documentation is, at this point, lacking. Once we have enough questions, we'll just ask them.

There's no reason the EXT-LFC can't be one of the GPIO pins repurposed and they just neglected to mark it. It doesn't help that the version of the datasheet that mentions it has no pinout table or application diagrams, like the v0.3 (I think it was?) in chinese does.

EDIT: grammers.