Can you tell me what this means and

Does the master issue a general purpose request to see if anyone is listening ? I was wondering how the master can respond to the slave if the master doesn’t know the slaves address. Perhaps the slave announces itself when it attaches ? Very curious.

I don’t think anyone said that it could. The master only talks to known slaves. Your code needs to have the I2C
address. This sometimes comes up as an issue for I2C LCD displays where the user doesn’t know the address.
In that case they run the I2C scanner and it "goes out " and finds all the slaves and reports their address.
You could call it a “Slave Finder” but what with everything going on right now that might not be politically correct.
It’s best just to call it the I2C SCANNER.

Rp
It’s a sexual roleplay game where you take on the role of a character and do whatever it takes to earn a sexual response. It is a sexual relationship designed to provide for a sexual relationship of similar character. It is not a family relationship.

I thought RP would obviously mean ResistorPULLUP, but that’s just me.
And FYI, “RP” does NOT equal “RP”. (P is a SUBSCRIPT)

This reads verbally as “R sub P equals Resistor, pullup”

raschemmel:
There is a clue: “RP

My snide response aside, actually it does not. RP could be either Resistor Pull-Up or Resistor Pull-Down, although member AWOL says that there is no such thing as a Pull Down.

No, I never said there is no such thing as a pull down, because that would be stupid.

I’m not stupid.

No, I never said there is no such thing as a pull down, because that would be stupid.

RP could be either Resistor Pull-Up or Resistor Pull-Down, although member AWOL says that there is no such thing as a Pull Down.

Actually it could NOT be a pulldown because it is connected to VDD , which by definition is “UP”.
Just for the record, GND is “DOWN”. So if the resistor labeled RP had the lower end connected to GND, then it
would indeed be a “PULLDOWN” , but the image you posted shows it connected to Vcc ,(which is UP, just FYI)

TheMemberFormerlyKnownAsAWOL:
No, I never said there is no such thing as a pull down, because that would be stupid.

I’m not stupid.

I apologize for any offense AWOL, but that is how I read this.

There is no pulldown resistor on I2C, just a pullup.

The pullup is there because the open-collector can only pull down,

What AWOL is saying here is that “Open-Collector” is a reference to the COLLECTOR of a TRANSISTOR, WHICH
because it is the COLLECTOR, and the transistor is an NPN, it CANNOT be connected to GND (which is DOWN),
so , by definition, an NPN transistor collector can only be pulled UP (like to Vcc).
In order for this to make sense to you , you would first need to know what a transistor is and how it works.
And secondly, you would need to know what “open-collector” means and what it’s application is. You would also
need to be aware that in electronics, the convention with respect to schematic illustration, is that the POSITIVE
supply (Vcc/Vdd) is at the TOP of the page and the GND or negative supply is at the bottom of the page. Hence
the origin of the “up” in “pullup” or the “down” in “pulldown”.

Do you ?

raschemmel: What AWOL is saying here is that "Open-Collector" is a reference to the COLLECTOR of a TRANSISTOR, WHICH because it is the COLLECTOR, and the transistor is an NPN, it CANNOT be connected to GND (which is DOWN), so , by definition, an NPN transistor collector can only be pulled UP (like to Vcc). In order for this to make sense to you , you would first need to know what a transistor is and how it works. And secondly, you would need to know what "open-collector" means and what it's application is. Do you ?

No, I was hoping for clarity in the terms of the sketch, SDA, SCL, VCC, VDD, etc. And thank you

No, I was hoping for clarity in the terms of the sketch, , SDA, SCL, VCC, VDD, etc.

If by “No” you mean you do not know what a transistor is or how it works or schematic convention or what open-
collector means and why it is used, then clarifying the below is not going to explain a whole lot because knowing
everything I just mentioned is almost a requirement for understanding SDA,SCL,Vcc, and Vdd, . (Vcc and Vdd are
functionally the same thing except Vdd is used for CMOS and MOS circuits that use mosfets , whereas Vcc is used
when the circuit uses transistors. (that’s a simplistic definition)

Clarification
SDA: Signal name for the Serial Data I2C signal
SCL: Signal name for the I2C Serial Clock signal
Vcc (NOT shown in schematic posted)

VCC stands for “voltage at the common collector.”. The letter “V” on a circuit stands for the supply voltage. The letters “CC” indicate that the supply voltage is positive or negative.

What does Vee stand for?
VDD : Drain Supply Voltage
etc: et cetera et cetera ? (are there other terms you wanted clarified as well ?)

For single supply circuits Vee is replaced with GND. Vee was used with ECL that had a -5V supply and has not
been used since ECL was phased out. (it may still be in use somewhere but is largely obsolete.

Just for the record , I can barely remember the day I asked myself “What does Vcc mean ?” but unfortunately
there was no Google 40 years ago.

Vee is still in use for bipolar op amps negative supply.

I couldn't remember if op amps used -Vcc or -Vee.

Thanks again to all who are trying to help me understand this. And no offense meant Raschemmel, but I am hoping that I will not have to dig too deeply into why and how transistors work in order to get a sketch to work. My background is that I have a lot of experience designing programs((sketches) and making them work and I didn't need nor want to know what was needed (a. Pull rexistor) on the wire that connects the devices that will need to talk to each other. As Perry said, this is not ethernet but that was how I was coming at this. As if I were plugging a new slave device into a network and I might or might not need something called a resistor on the connection. That bit is a whole new concept and I cannot imagine why my simple little temperature sensor would need a resistance between me and the master. And what the heck do I do when I need 3, SDA and SCL connections and there is only 1 tiny little hole in the Master? Does that mean that I will need to tie them together somehow? I understand the addressing bit so that's a start, and the above schematic helps a bit. When I have tried something similar before,, it would had lead to smoke. Electronics stuff is weird and that bit about VCC (collector) being at the top of the page is very interesting. That explains why it is not V+ VCC must share a place with North. Isn't N(North) always at the top :=) ? Enough for now, I am going to go think about this in light of what y'all have tried to explain to me. Yes, Google is my friend but you need to know what to ask.

" Does that mean that I will need to tie them together somehow? I "
Yes. They are all tied together on the ‘bus’. Google it.
That’s the function of open collector. All devices share the SDA & SCL lines.
Vcc is V+ but your schematic is a MOS schemaic so it uses Vdd (Drain Supply) because mosfets don’t have collectors. They have Drains. But maybe that’s TMI. No one can force you to learn anything until you are ready to learn it. As you recall, you asked us what it means. It’s almost impossible to explain why pullups are needed for I2C without talking about ‘open-collector’ and it’s hard to discuss ‘open-collector’ without discussing transistors. Some people like to be perfectly correct so they will insist it’s ‘open-drain’ not ‘open-collector’ but most people just call it open-collector when talking about I2C. Each signal needs one resistor so if you have less than 10 ‘little things’ then you only need to put pull-UP resistors on one of them. Also, there probably won’t be any ‘holes’ because ‘through-hole’ technology has been mostly replaced by surface mount so there will be pads for SMD resistors that will have numbers instead of colored stripes. That’s progress…

Thanks again for your patience. My TMI starts when you start talking about drain vs collector. I am only interested in SDA and SCL as they are my interface to the sketch (program). The sketch is complicated enough. Referring to the sketch that I posted, it shows VDD connected to the SDA and SCL buss. I am only aware of +5V and +3.3V as furnished by the Arduino, or the +5V as furnished by my external power supply. There are no VDD and VCC indicated on the board. So, using a breadboard, i guess that I will wire the SDA from the ESP32, and the SDA from each device to the breadboard, and then wire the breadboard to a 4.7k resistor to the +5V. And keep a fire extinguisher handy. We'll see what happens.

What makes you think pulling a 3.3V-only capable pin to 5V is a good idea?

Don’t have a fire-extinguisher on standby, just a credit card.

There are no VDD and VCC indicated on the board.

As mentioned before, your boards are MOS so Vcc does not apply, Also, "Vdd" and "Vcc" are generic terms that represent whatever power supply you are using. The 'little things' have some specific power supply voltage that they operate at, and whatever that is, that is "Vdd". It's really that simple. I looked at your OP and I didn't see any link for the 'little things'. Please post a vendor link so we can look at the supply voltage of the 'little things'.

What makes you think pulling a 3.3V-only capable pin to 5V is a good idea?

Don't have a fire-extinguisher on standby, just a credit card.

I was trying to get to that detail but I have to edge the information in little by little to avoid TMI.

Sometimes it is better to have TMI than TLM

TLM ?

“Too Little Money”

TheMemberFormerlyKnownAsAWOL: What makes you think pulling a 3.3V-only capable pin to 5V is a good idea?

Don't have a fire-extinguisher on standby, just a credit card.

Hahah, that is probably why I have spent way too much $$$ on this "intermediate" grade project. And I don't usually do just guess and plug.. What I do is look at the pin descriptions for the addon devices to see what they say as to voltage. Mine are: BNO055 VIN 3.3-5.0V (easy to understand)

PCA9685 VCC This is the logic power pin, connect this to the logic level you want to use for the PCA9685 output, should be 3 - 5V max!

So it sounded like I could use either 3.3 or 5

However when I read the following it gave me pause cause I had no idea what I had to do if anything.

It's also used for the 10K pullups on SCL/SDA so unless you have your own pullups, have it match the microcontroller's logic level too! Does this mean that whatever voltage the Feather ESP32 or Feather Huzzah uses as a logic level, I should use the same ? Never mind that I have no idea what that means. I know of only 1, voltage on my microcontroller. 5V from the USB or battery, though the board does furnish 3.3V output. HAH ! I just did a google search of Feather ESP32 and Feather Huzzah, logic level and it came back as 3.3V. So maybe I will need to do some rewiring. I think writing programs is easier.

No comment.