I modify the code from js-stk500 to work from browser with web serial API. but I can't makr Arduino CLI to work in browser. Is that possible?

That really anewer my question. I just self learner. By missing that information make my life a hard time figured out how things work. Thank to you.

So all ESP32 have build-in bootloader right? means I don't need to re-install it ever? I never see someone done that before

@RowanP That one confuse me. so with one bootloader esp32 can work with all environment??? or the system not required bootloader at all???

I think bootloader only use with stk500 Serial UART protocol upload.

Both usb-asp and Arduino as ISP is the programmer which be able to upload sketch either bootloader. In my question it do the same job to uploader but the chip not answer to usbasp but it work fine with arduino as isp. my inspectation is is about factory setting clock speed of the chip the corelate to programmer clock speed. but still no clue.

Wow, never think that was firmware problem. I doesn't need the fix I want the explanation.

@JRobert, yes I use Arduino UNO with Arduino 1.1.13

@EdgarBonet that why I seraching for solution to make A “silent” TX become high impedance. it should be possible by software some how.

You hardware setup can prvent damage but I wonder if one slave send no data (given High signal) will the data get voltage divider effect that divide signal amplitude to half?