USB 2.0 Test Modes and Their Application

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USB 2.0 Test Modesand Their Application

• Jon LuekerIntel Corporation

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Link Integrity Strategy

• Define necessary and sufficient set of
  specifications for cables, upstream-facingports,
  and downstream-facing ports
• Define reproducible tests which allow testingof
  each element in isolation
• Define required test modes which allow teststo
  be performed with standardized equipmentand
  techniques

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Specifications for aHigh-Speed Transmitter

• Source impedance
• Clock frequency
• DC Levels into reference load
• Transmit eye pattern into reference load
• At pins of transceiver (guideline)
• At USB receptacle (if no captive cable)
• At end of cable (if cable is captive)
• Minimum allowable rise/fall time

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Specifications for aHigh-Speed Receiver

• DC termination voltage and resistance
• Squelch threshold level
• Disconnect threshold level
• TDR (AC loading) limits
• Worst case eye patterns which mustbe recoverable
• At pins of transceiver (guideline)
• At USB receptacle (if no captive cable)
• At end of cable (if cable is captive)

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Specifications for USB Cable

• Maximum length and delay per meter(delay spec
  added in USB 1.1 ECN)
• Differential and common mode impedance (common
  mode spec added in ECN)
• Skew (tightened to 100 ps from 400 ps in ECN)
• Maximum allowable loss (added 200MHzand 400MHz
  points in ECN)

USB 1.1 cable specification was updated in
November, 1999, to guarantee specs which were
being met typically
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Test Modes

• High-speed capable devices/hubs must support test
  modes
• Test modes enable repeatable testing
• SetFeature(TEST_MODE) and SetPortFeature(PORT_TEST
  ) requests provide standard means of entering
  mode
• Exit action is also standardized
• Upstream facing port power cycle
• Downstream facing port hub reset

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Test Mode Test_SE0_NAK

• Port enters and remains in the high-speedidle
  state
• Regular actions, such as suspending,are
  inhibited
• Upstream-facing ports must respond to anyIN
  token packet with a NAK handshake(if CRC is
  correct)

Allows Testing of Output Impedance (AC and DC),
Termination Voltage, and Receiver Sensitivity
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Test Modes Test_Jand Test_K

• Port enters and remains in the high-speedJ or K
  state
• Regular actions, such as suspending,are inhibited

Allows Testing of Output Voltage and Output
Impedance When Each Output Is High or Low
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Test Mode Test_Packet

• Port repetitively transmits defined test packet
• Packet is designed to contain the full range of
  pattern frequencies and duty factors

Allows Testing of Output Eye Patterns, Jitter,
Waveform Parameters, and Frequency
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Test Mode Test_Force_Enable

• Applies only to downstreamfacing hub ports
• Required behaviors apply even if no deviceis
  attached
• Port must be enabled in high-speed mode
• Downstream packets must be repeated to the port

Allows Testing of Disconnect Threshold
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Example Testing aSelf-Powered Device

• Testing Input Impedance and Termination Voltage
• Testing Output Levels
• Testing Transmit Waveforms
• Testing Receiver Sensitivity
• Testing Squelch Threshold

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Example Testing Input Impedance and Termination
Voltage

• Attach DUT to USB 2.0 host controller
• Reset the device and then issue request to place
  device in Test_SE0_NAK mode
• Unplug cable from device and replace it with test
  cable/fixture
• Measure DC output voltage on each line
• Measure DC resistance on each line
• Perform differential TDR test on outputs

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Example TestingOutput Levels

• Attach DUT to USB 2.0 host controller
• Reset the device and then issue request to place
  device in Test_J mode
• Unplug cable from device and replace it with test
  cable/fixture
• Measure output voltages into 45 Ohm loadsto
  ground
• Repeat using Test_K

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Eye Pattern Test Fixture
Transmitter/Receiver Test Fixture
Transmitter Test Attenuation Voltage at Scope
Inputs 0.760 Voltage at Transmitter
OutputsReceiver Test Attenuation Voltage at
Receiver Inputs 0.684 Voltage at Data
Generator Outputs
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Example TestingTransmit Waveforms

• Attach DUT to USB 2.0 host controller
• Reset the device and then issue request to place
  device in Test_Packet mode
• Unplug cable from device and replace it
  withhigh-frequency test cable/fixture
• Measure rise/fall time
• Capture single, complete occurrence of
  testpacket on a transient capture instrument
• Perform eye pattern analysis on waveform record

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Example Testing Receiver Sensitivity and Squelch
Threshold

• Attach DUT to USB 2.0 host controller
• Reset the device and then issue request to
  placedevice in Test_SE0_NAK mode
• Unplug cable from device and replace it with test
  cable/fixture
• Using data generator, apply IN token packet while
  varying amplitude, frequency, and injected jitter
• Using a differential high-impedance probe,
  monitor the cable to see under which conditions
  device responds with NAK handshake

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