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).

參考資料 ^^^^^^^

http://www.zeroplus.com.tw/E-paper/201112/images/201112-USB20ProtocolAnalyzer.pdf