Understanding non-connected resistors in reference schematic

[Scalpel78]

Hi,
when looking at the schematics for the reference board, ESP Core Board v2, I see there are four non-connected resistors.

R19 and R20 seems to optionally connect RTS and CTS with GPIO13 and GPIO15.
R7 and R5 are optional pull-up, and pull-down, resistors for GPIO0 and GPIO2.

What is the purpose of these optional resistors? I'm asking because I'm making my own ESP-WROOM-32 board, and want to understand if I should include these or not.

[Scalpel78]

And another question about the reference board - is it correct that the button for GPIO0 is no longer needed?

[rudi ;-)]

Hi,
when looking at the schematics for the reference board, ESP Core Board v2, I see there are four non-connected resistors.

R19 and R20 seems to optionally connect RTS and CTS with GPIO13 and GPIO15.
R7 and R5 are optional pull-up, and pull-down, resistors for GPIO0 and GPIO2.

What is the purpose of these optional resistors? I'm asking because I'm making my own ESP-WROOM-32 board, and want to understand if I should include these or not.

i try to say it with other words:
if you want use gpio 0 as output gpio with pulled up resistor
you can not flash it cause you can not pull down it.

so the things with optional NC resistor is,
how you want use the pins for it. in this design, we use the things like they configured/connected.

in a develop board, the gpio 0 pulled up resistor then is NC
in a enduser board, the gpio 0 pulled up resistor perhabs then is connected ( cause it is end user )

see in the pin list, a pin can have more functions.
and each function need other HW config
see Touch Pins ( capazitator ) - example

best wishes
rudi

[Scalpel78]

Hi rudy, ok, so let me see if I understand correctly.

GPIO0 and GPIO2 are strapping pins. GPIO0 needs to be high when flashing. And when R7 is not connected, it is driven high by the internal pull-up resistor. After booting it behaves like a generic push-button. Correct? Hmm, no, I still don't get it. Cause if so, then the only difference when R7 is connected is if the pull-up is done by internal or external resistor. I don't see why.

In the ESP-WROOM-32 datasheet, in the table describing the strapping pins it mentions "SPI Flash Boot" and "Download Boot", but I don't understand the difference between those two.

Also, with regards to the RTS and CTS pins. They are by default not connected, and thus have no purpose. If those are connected to GPIO13 and GPIO15...then what? When is that useful?

[WiFive]

In the ESP-WROOM-32 datasheet, in the table describing the strapping pins it mentions "SPI Flash Boot" and "Download Boot", but I don't understand the difference between those two.

SPI Flash Boot = normal operation
Download Boot = firmware update from esptool

Also, with regards to the RTS and CTS pins. They are by default not connected, and thus have no purpose. If those are connected to GPIO13 and GPIO15...then what? When is that useful?

If you want to use those flow control pins from the USB/serial chip for something, testing hw flow control or some other signal.

[rudi ;-)]

bootstrapping_pins.png (51.43 KiB) Viewed 9587 times

In the ESP-WROOM-32 datasheet, in the table describing the strapping pins it mentions "SPI Flash Boot" and "Download Boot", but I don't understand the difference between those two.

SPI Flash Boot means,
esp32 is booting and read the Firmware from the connected SPI Flash
for this, the boot straping pins are for
GPIO0 1 (high)
GPIO2 don't care

Download Boot means,
esp32 is in "download" mode and waiting now for uploading the firmware
GPIO0 0 (low)
GPIO2 0 (low)

GPIO0 and GPIO2 are strapping pins. GPIO0 needs to be high when flashing.

what you mean with flashing?
if you mean "boot from the spi flash" then is right
if you mean "upload your firmware" then is wrong

the other question i will let it open, perhabs you can now check by self
if not, write, so we see in it again

best wishes
rudi

edit: WiFive was faster

[rudi ;-)]

13_15.png (70.56 KiB) Viewed 9585 times

Also, with regards to the RTS and CTS pins. They are by default not connected, and thus have no purpose. If those are connected to GPIO13 and GPIO15...then what? When is that useful?

edit: btw, you can allways pullup, pulldown the pinheader pins like you need.
the example on gpio13, gpio15 is, if you want to use it as RTS, CTS
you can do it by connect GPIO13, GPIO15 on the pinheader.
that in the shematic there is no Resistor value, is, cause you can use this pins in variations of bootstrapping and using




cause this is what you want to do with it.

example:
if you want use it for the sd card driver
you pulled up
GPIO13 HS2_DATA3 / SD_DATA3
GPIO15 HS2_CMD / SD_CMD

if you want use it for example as GPIO input pins,
and want config the trigger ( ISR ) on a raise edge
then you can not pullup the pins, you mus pulldown

its like you want to use it, so you must config and solder it.

some pins are functionally
example then the pin GPIO15,
if you need this by set your timing too for SDIO
then you need to solder a switch for it on bootstrappmode.
after booting the switch give free your settings to your GPIO15 mode like you need or want ( pullup, pulldown )

hope this helps
best wishes
rudi