Originally Posted by
ShelGame
Yes, the 12v comes from the outside world. The SBEC doesn't generate that itself. Correct, we are protecting the FTDI chip from the 12v we put on the Rx line to bootstrap the SBEC.
'For the SBEC, the bootstrap line is multiplexed with the Rx line' is more technically correct. But, the average person doesn't know what 'multiplexing' is. There is a circuit inside the SBEC that protects the Rx line on the processor from the 12v, while also sending 5v to the MODE pins. So, when the SBEC is turned on, the processor starts in the special bootstrap mode.