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May 8, 2001 2
USB 2.0 Signal Protocols
USB 2.0 Signal Protocols
Jon LuekerJon LuekerIntel CorporationIntel Corporation
May 8, 2001 3
Protocol Requirements Similar to USB 1.1Protocol Requirements Similar to USB 1.1
Data encodingData encoding Packet Start/End delimitersPacket Start/End delimiters Connect/Disconnect detectionConnect/Disconnect detection Suspend/ResumeSuspend/Resume ResetReset Speed detectionSpeed detection
May 8, 2001 4
NRZI Data EncodingNRZI Data Encoding
Same data encoding as LS and FS modesSame data encoding as LS and FS modes 0 is encoded as a transition, 1 as no transition0 is encoded as a transition, 1 as no transition Bit stuffing inserts a 0 after every 6 consecutive 1’sBit stuffing inserts a 0 after every 6 consecutive 1’s Maximum number of symbols without transition is Maximum number of symbols without transition is
7 (except EOP)7 (except EOP) Bit stuffing assures sufficient transitions to keep Bit stuffing assures sufficient transitions to keep
DLL locked onto data streamDLL locked onto data stream
May 8, 2001 5
High-Speed SOPHigh-Speed SOP
HS Idle K J K J K J K J K J K K DataHS Idle K J K J K J K J K J K K Data
Receiver squelched - Differential envelope
below 100mV
Receiver squelched - Differential envelope
below 100mVDifferential envelope
exceeds 150mV - reception enabled within
four symbol times
Differential envelope exceeds 150mV -
reception enabled within four symbol times
Clock recovery circuit must lock in time to detect end of SYNC
Clock recovery circuit must lock in time to detect end of SYNC
End of SYNCdetected, receiver
begins datarecovery
End of SYNCdetected, receiver
begins datarecovery
HS SYNC Field - 32 bitsHS SYNC Field - 32 bits
May 8, 2001 6
High-Speed EOPHigh-Speed EOP
Data Bit Stuff Error SE0Data Bit Stuff Error SE0
Normal HS data transmission with
NRZI encodingand bit stuffing
Normal HS data transmission with
NRZI encodingand bit stuffing
First bit of the EOPfield is a transitionFirst bit of the EOPfield is a transition
EOP field is a bitstuff violation
EOP field is a bitstuff violation
After EOP, lines return to Idle
state and receiver is squelched
After EOP, lines return to Idle
state and receiver is squelched
HS EOP FieldHS EOP Field
May 8, 2001 7
Disconnect DetectionDisconnect Detection
Basic idea is to check for higher than normal signal voltages on the Basic idea is to check for higher than normal signal voltages on the differential pair differential pair
Higher voltages will result when device terminations are removed - Higher voltages will result when device terminations are removed - nominal increase is a jump from 400mV to 800mVnominal increase is a jump from 400mV to 800mV
Check is performed during last 8 bits of EOP of uSOF framesCheck is performed during last 8 bits of EOP of uSOF frames uSOF EOP is lengthened to 40 bits to make this mechanism reliable uSOF EOP is lengthened to 40 bits to make this mechanism reliable
- duration must be longer than round-trip time of- duration must be longer than round-trip time ofmaximum length cablemaximum length cable
DeviceDisconnection
DeviceDisconnection
DisconnectionVoltage
Threshold
DisconnectionVoltage
Threshold
DisconnectDetected
DisconnectDetected
May 8, 2001 8
Suspend from HSSuspend from HS
HS device suspend is initiated when a deviceHS device suspend is initiated when a devicesees no activity from upstream port for 3.0mssees no activity from upstream port for 3.0ms
Between 3.0 – 3.125ms, device transitions from HS to FSBetween 3.0 – 3.125ms, device transitions from HS to FS Device must differentiate between SE0 (reset)Device must differentiate between SE0 (reset)
and Idle (suspend)and Idle (suspend) 100 – 875us after reversion to FS, device tests line for 100 – 875us after reversion to FS, device tests line for
SE0 (Reset) vs. FS J (Suspend)SE0 (Reset) vs. FS J (Suspend) If FS J, device goes into Suspend followingIf FS J, device goes into Suspend following
FS behaviorsFS behaviors
May 8, 2001 9
Timeline for SuspendTimeline for Suspend
FS idle (J)FS idle (J)HS Idle (device still in HS)HS Idle (device still in HS)
100-875 μs3.0-3.125 ms
Devicerevertsto FS
Start ofInactivity
μSOFμSOF
HS
Hub
HS
Dev
ice
D–
D+
Device tests bus for FS J and then goes
into suspend
Start of Suspend Signaling(Hub port goes to FS Idle)
May 8, 2001 10
ResumeResume
For a device suspended while in HS, ResumeFor a device suspended while in HS, Resumeis a FS K asserted for a minimum of 20ms is a FS K asserted for a minimum of 20ms followed by a transition to SE0followed by a transition to SE0
At end of Resume (while port issuing resume At end of Resume (while port issuing resume asserts SE0) hub and device transitionasserts SE0) hub and device transitionto HS operationto HS operation
Since SE0 and HS Idle are equivalent on the bus, Since SE0 and HS Idle are equivalent on the bus, there is no “glitching” during this transitionthere is no “glitching” during this transition
uSOF’s commence in time to prevent a returnuSOF’s commence in time to prevent a returnto suspendto suspend
May 8, 2001 11
Timeline for ResumeTimeline for Resume
< 3.0 ms
Hub Drives SE0 for Two LSBit Times, Enters HS
HS
Hub
HS
Dev
ice
FS KFS K HS idleHS idle μSOFμSOF
D+
Device seesfirst activity
Start ofResume
Signaling
D–
FS idleFS idle
> 20 ms
Device ResumedIn HS
< 1.33 μs
SE0SE0
< 1.33 μs
May 8, 2001 12
Reset/Speed Detection ProtocolReset/Speed Detection Protocol
High-speed capable devices are reset by 10msHigh-speed capable devices are reset by 10msof continuous SE0 (same as USB 1.1)of continuous SE0 (same as USB 1.1)
During Reset, a high-speed capable deviceDuring Reset, a high-speed capable device“chIRPs” to the hub“chIRPs” to the hub
If a USB 2.0 hub detects this chIRP, it completesIf a USB 2.0 hub detects this chIRP, it completesthe handshake by chIRPing back to the devicethe handshake by chIRPing back to the devicewithin the Resetwithin the Reset
If the handshake is completed during Reset,If the handshake is completed during Reset,both hub and device come out of Reset inboth hub and device come out of Reset inhigh-speed modehigh-speed mode
May 8, 2001 13
Reset Handshake SignalingReset Handshake Signaling
Device chIRP is a ChIRP K (detected with hub’sDevice chIRP is a ChIRP K (detected with hub’shigh-speed receiver)high-speed receiver)
Device chIRPs by driving current in D- line while Device chIRPs by driving current in D- line while leaving D+ pullup in place and leavingleaving D+ pullup in place and leavingterminations inactiveterminations inactive
Hub chIRP is a series of alternating ChIRP J’sHub chIRP is a series of alternating ChIRP J’sand K’sand K’s
Hub chIRPs by driving current into D+ or D- lineHub chIRPs by driving current into D+ or D- line Reference state machines included in Appendix CReference state machines included in Appendix C
May 8, 2001 14
Timeline for ResetTimeline for Reset
μSOFμSOF Device ChIRPDevice ChIRP Hub ChIRPHub ChIRP
D+
D–
3.0-3.125 ms 100-875 μs > 1.0 ms
< 7.0 ms
< 100 μs 100-500 μs
> 10 ms
Device ChIRP
Start ofReset
Device EntersHS < 500 UsAfter DetectingHub ChIRP
Start ofReset
End ofReset
End ofHub ChIRP
Start ofHub ChIRP
μSOFμSOF
Hub
Dev
ice
SE0SE0 SE0SE0SE0SE0 HS idleHS idle
Devicegoes
into FS
Devicetests for
SE0