Holding button during flashing ESP

[Deouss]

I just bought some cheap pcb boards with usb to ttl converter and nice buttons.
After soldering esp chip and testing board I noticed I have to hold the key button and all was fine.
I have another firebeetle board and it doesn't need that.
What is the rule or reason for that? Does it depent on the onboard chip or design?
Or is it type of built in feature on the esp chip or usb?

[WiFive]

Yes there is a special boot circuit and not all boards have it

[Deouss]

Can you tell me more what circuit it is?
What should I look for?

[WiFive]

Basically the parts to the left of the USB bridge label

[Deouss]

So I am guessing it is all on the uart\usb chipset.
Like a built-in feature than comes with IC

[ESP_Angus]

So I am guessing it is all on the uart\usb chipset.
Like a built-in feature than comes with IC

No, some additional circuitry is added (where WiFive mentions, look for the label on the PCB itself) to coordinate the automatic reset.

You can read about the details here:
https://github.com/espressif/esptool/wi ... bootloader

If you download (for example) the ESP32-DevKitC-V4 reference design from the downloads page and open the reference schematic PDF, you can see the equivalent connections in the bottom left of the page/