May 16, USB 2.0 Signal Protocols Jon Lueker Intel Corporation

May 16, Protocol Requirements Similar to USB 1.1 w Data encoding w Packet Start/End Delimiters w Connect/Disconnect detection w Suspend/Resume w Reset w Speed detection

May 16, NRZI Data Encoding w Same data encoding as LS and FS modes w 0 is encoded as a transition, 1 as no transition w Bit stuffing inserts a 0 after every 6 consecutive 1’s w Maximum number of symbols without transition is 7 (except EOP) w Bit stuffing assures sufficient transitions to keep DLL locked onto data stream

May 16, High-Speed SOP SE0 K J K J K J K J K J K K Data Receiver squelched - Differential envelope below 100mV Differential envelope exceeds 150mV - reception enabled within four symbol times Clock recovery circuit must lock in time to detect end of SYNC End of SYNC detected, receiver begins data recovery HS SYNC Field - 32 bits

May 16, High-Speed EOP Data Bit Stuff Error SE0 Normal HS data transmission with NRZI encoding and bit stuffing First bit of the EOP field is a transition EOP field is a bit stuff violation After EOP, lines return to Idle state and receiver is squelched HS EOP Field

May 16, Disconnect Detection w Basic idea is to check for higher than normal signal voltages on the differential pair w Higher voltages will result when device terminations are removed - nominal increase is a jump from 400mV to 800mV w Check is performed during last 8 bits of EOP of uSOF frames w uSOF EOP is lengthened to 40 bits to make this mechanism reliable - duration must be longer than round-trip time of maximum length cable Device Disconnection Device Disconnection Voltage Threshold Disconnection Voltage Threshold Disconnect Detected Disconnect Detected

May 16, Suspend from HS w HS device suspend is initiated when a device sees no activity from upstream port for 3.0ms w Device must differentiate between SE0 (reset) and Idle (suspend) w At 3.0ms, device transitions from HS to FS w 2.5us later, device tests line for SE0 (Reset) vs. FS J (Suspend) w If FS J, device goes into Suspend following FS behaviors

May 16, Resume w For a device suspended while in HS, Resume is a FS K asserted for a minimum of 20ms followed by a transition to SE0 w At end of Resume (while port issuing resume asserts SE0) hub and device return to HS operation w uSOF’s commence in time to prevent a return to suspend

May 16, Reset/Speed Detection Protocol w High-speed capable devices are reset by 10ms of continuous SE0 (same as USB 1.1) w During Reset, a high-speed capable device “chirps” to the hub w If a USB 2.0 hub detects this chirp, it completes the handshake by chirping back to the device within the Reset w If the handshake is completed during Reset, both hub and device come out of Reset in high-speed mode

May 16, Reset Handshake Signaling w Device chirp is a Chirp K (detected with hub’s high-speed receiver w Device chirps by driving current in D- line while leaving D+ pullup in place and leaving terminations inactive w Hub chirp is a series of alternating Chirp J’s and K’s w Hub chirps by driving current into D+ or D- line w Reference state machines included in Appendix C