ESP8266 Community Forum

- Thu Jun 25, 2015 3:01 pm #21674

It shows GPIO2 floating and I can confirm this definately works .
[...]
Can anyone else define where that pin should be and why please. It appears that both might work and maybe the truth table should be ammended to "x" don't care ?

I prefer trusting a spec sheet than people testimonies. the Boot process table from the above link is proably a copy/paste from Espressif specs. It should NOT be amended to please end-users.
Been in electronic engineering for decades, the four different possible connections for an input : L, H, X and NC. BTW, X doesn't mean floating, it means "irrelevant". Not connecting a X input can still be troublesome, since EMI/RFI can disturb the input, and even destroy it if EMI/RFI is too high. We should never leaving inputs floating, except if specs says NC.

Additionnally, if the table says to put it to HIGH, even if there is currently no mode in the table that use it with LOW, it doesn't mean Espressif can decide in a future to use that for an additionnal mode of boot process, let's says for example thru an I2C bus. So, to respect backward compatibilty, we should follow the specs to the "letter".

EDIT : BTW, and I've just try it out : if GPIO2 had a X instead of H, then that would mean that we can place to LOW, but right now, in such case it does NOT boot any more ! If leaving it floating works, it is simply that, like in the old days of TTL, floating is quite the same as HIGH (except about EMI potential issue). Right now, it is confirmed : Espressif really spec it that a HIGH level is REALLY required on GPIO2 !

- Fri Jun 26, 2015 12:17 am #21717 Deleted

Last edited by tytower on Mon Jun 29, 2015 3:44 pm, edited 1 time in total.

Get you modules here:

https://www.banggood.com/custlink/KvGGhGF4wG

- Fri Jun 26, 2015 1:28 am #21722 Moin tytower,

please accept that you are wrong with this. There is a difference between floating and connecting.
There is a difference between "don't care" (X) and "floating".
You are trying to help a lot of people but here you are indeed misleading.
A floating pin especially with some trace and possibly even a connector works like an antenna.
Using pull-ups/pul-downs help to work against catching a signal from the environment.
Take an oszilloscope to get an impression what difference a resistor makes.
Or build a darlington based detector to amplify the antenna effect to some led lighting.
If your hand is just getting nearer/away from the antenna you see a difference.

Please don't mislead people. Works for me is no replacement for application notes and rules.
I have been corrected recently here on an issue I believed I know and I based my tipps on.
I was wrong because the espduino guy did a clever adaption of the arduino stuff to espduino.
There is a lot to learn outside and the internet provided great new way of doing things.
But it does not change the rules of physics.
It frightens me if I see people just starting with electronis "designing" PCB layouts that are connected to the
house mains current without proper fusing, distances, etc. Or switching machines on and off using
an esp8266 with just an relais and no hardware/software protection schemes.
People will die because of this.

Cal

Get your modules here:

https://www.banggood.com/custlink/KvGGhGF4wG

- Fri Jun 26, 2015 3:23 am #21731 Seems a few people have barrows to push around the place Cal . As a full call ,ham radio operator in Australia the study and knowledge of radio and electronics required is extensive . I fancy myself as a bit of a Yagi specialist . I understand antennas. Normally I would not reference that fact but your speech necessitates it . look me up . So as they say don't tell me about boats.Hi Hi

I'm a bit disapointed with your speech though. Its a bit like trying to kick a man when he's down and thats not acceptable conduct here in Australia and in many parts of the world still. Things like that are never forgotten .

Now on the technical side, not connecting the pin as per the connection diagram not only works for me, but for many many others I gather .Look around . You can take it high if you feel that is safer but it is incorrect to say I am misleading anybody by telling them to leave it unconnected. At no point have I said its a "don't care " thats just been made up and shoved in for effect . Don't care is entirely different

I've also said that I am going to make many mistakes in posts. That's the nature of the device we bought to play with and the learning forum we joined . I hope you might see the merit in my post.

Last edited by tytower on Mon Jun 29, 2015 11:48 pm, edited 1 time in total.

Get you modules here:

https://www.banggood.com/custlink/KvGGhGF4wG