版本 dad2743c97cc664eb9063eac93b047626703ae11

embedded/USB

Changes from dad2743c97cc664eb9063eac93b047626703ae11 to ddf0a60c155b44867eeec0875e0f972702189500

---
title: usb
...

標準USB介面
^^^^^^^^^^

USB插頭
USB訊號使用分別標記為D+ 和D- 的雙絞線傳輸，它們各自使用半雙工的差動訊號並協同工作，以抵消長導線的電磁干擾。

ps. 差動訊號：一條為 high 則另一條為 low 

temporal notes
^^^^^^^^^^^^^^^
.. image:: /USB_block_diagram.png

 1. AHB(Advanced High-performance Bus)
 2. DP/DM description -- in reference manual 30.3.2
    - DP/DM integrated pull-up and pull-down resistors controlled by the OTG_FS core depending on the current role of the device. As a peripheral, it enables the DP pull-up resistor to signal full-speed peripheral connections as soon as VBUS is sensed to be at a valid level (B-session valid). 
    - In host mode, pull-down resistors are enabled on both DP/DM. Pull-up and pull-down resistors are dynamically switched when the device’s role is changed via the host negotiation protocol (HNP).