mano1979 wrote:You mean IC1? That is the ams1117 3.3V (lm1117) voltage regulator.
Otherwise there is SJ1. That is a solderpad for choosing wich pin to pull down to 3.3v. (Rx or tx). Just solder the pad you want to pull down to the middle pad.
##[x] RXD
[x]## TXD
Yes I ment sj1. Ok its clear now. But usualy one wants both tx and rx to be level shifted isn't it so? So why to shift onlyone signal?