|
今天去翻ST官方手册,发现里面有这么一段话:
Q: According to the USB specification (FS driver characteristics), when the full-speed driver is/is not part of ahigh‑speed capable transceiver, the impedance of each of the drivers must be in the range 40.5 to 49.5 Ω/28 to44 Ω, respectively. Are the STM32 devices embedding these matching resistors?
A: Yes. On the internal USB PHYs, the matching output impedance is already embedded in the pad transceiverand is in line with the USB specification. No external resistors are needed.
翻译过来大概就是说STM32芯片内部已经做了阻抗匹配,无需在信号线串电阻,官方没说具体哪个型号,应该所有芯片都是这样。
然而我看了很多开发板原理图,上面都对D+D-串了个10几20欧的电阻,所以说有没有串电阻的必要,不串就会影响通信吗?还是说串电阻本身就是画蛇添足
|
|