SLLSFC6B November 2021 – July 2022 ISOUSB111
ISOUSB111 supports symmetric operation. Normally, UD+ and UD- are upstream facing ports and connect to a host or hub. DD+ and DD- are downstream facing ports and connect to a peripheral. However, it is also possible to connect UD+ and UD- to a peripheral and DD+ and DD- to a host or hub. Whichever side sees a connect first (D+ or D- pulled up to 3.3V) becomes the downstream facing side. This feature enables implementation of dual-role port (for eg. Type-C dual-role port) and role-reversal (for eg. OTG Host Negotiation Protocol - HNP). Refer to How to Implement an Isolated USB 2.0 High-Speed, Type-C® DRP application note for details. In the rest of this document, DD+/DD- are treated as downstream facing ports, and UD+/UD- as upstream facing ports, but the various operations and features described are equally applicable if this assignment is swapped.