Page 1 of 2
D+ D- are differential? How is this connected to ESP8266?
Posted:
Fri Aug 12, 2016 1:46 pmby RichardS
Just wondering? I know it works with I/O on AVR, but I think people would like to know the details of this...
RichardS
Re: D+ D- are differential? How is this connected to ESP8266
Posted:
Fri Aug 12, 2016 8:59 pmby cnlohr
They are kind of differential. During normal data they are differential, but end-of-packet is specified by both lines going low for two time slices.
The two wires are directly connected to two adjacent GPIOs (in the low-speed mechanism). Only thing in addition is I wired a 1.5k resistor between d- and 3.3v.
*EDIT* Supposedly, there's also supposed to be resistors in line with D+/D- -- though for short runs I don't think it's needed.
Re: D+ D- are differential? How is this connected to ESP8266
Posted:
Sat Aug 13, 2016 10:43 amby RichardS
So if its differential the voltage swings must be large enought to cause 0 and 1 transistions on the I/O, if the 2 differential pairs hung out a say Vcc/2 and just swung north and south of one another I can not see how the I/O would "see" that.....
RichardS
Re: D+ D- are differential? How is this connected to ESP8266
Posted:
Sat Aug 13, 2016 1:21 pmby cnlohr
Oh the swing is quite sufficient, especially on low-speed. Crystal clear. I was having trouble at full-speed though where it wasn't triggering the interrupts reliably :-/. I guess yet another reason it may not have been meant to be.