OK. It tooks me 10 hours to make USB commmunication works. Here, I was just able to get 3.6 V, 1 Watt zener diodes. I’ve never been able to make it work.
Then I found 3.2 V, 1/4 Watt zener diodes. Didn’t work. After many many attemps, I’ve begun to use a scope to have an idea of what was going on… and it worked! It was due to the scope impedance. So, I’ve added a 500 k resistance between ground and D-. And it works!!
Also, I power the uC from USB. I need to put a 0.1 uF in parallel to Vcc and Gnd.
Then I found 3.2 V, 1/4 Watt zener diodes. Didn’t work. After many many attemps, I’ve begun to use a scope to have an idea of what was going on… and it worked! It was due to the scope impedance. So, I’ve added a 500 k resistance between ground and D-. And it works!!
Also, I power the uC from USB. I need to put a 0.1 uF in parallel to Vcc and Gnd.