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TUSB2046B Errata
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格式:rar |
大小:19 |
2010-09-09
安德森大
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By the intent of the USB specification (shown in Figure 7-19), the speed should be determined by
sampling the DP or DM line following a 100ms debounce interval after either signal (DP or DM) first
crosses the V IH threshold. The TUSB2046B (TUSB2077A, TUSB2036) actually samples the speed at the
irst V IH crossing and latches this value. This issue has only been observed recently with newer devices
hat either drive DM high or show excessive ringing during the initial connection, hence causing the speed
detection to be seen as low speed by the TUSB2046B (TUSB2077A, TUSB2036). Note that this device is
used extensively in the USB1.1 Goldtree suite, and this issue was never revealed, further pointing to the
act that some newer devices have less control on DM than previous devices, although this is allowed by
he USB specification. TI has no planned fix in the pipeline, but wants users to be aware of this issue,
which can easily be avoided by guaranteeing that DP be asserted high before DM. In the event that a
alse low speed detection is observed, the situation can be resolved by performing a
CLEAR_PORT_FEATURE(PORT_ENABLE) followed by a RESET_PORT in the software driver,
assuming both DP and DM are now stable.
sampling the DP or DM line following a 100ms debounce interval after either signal (DP or DM) first
crosses the V IH threshold. The TUSB2046B (TUSB2077A, TUSB2036) actually samples the speed at the
irst V IH crossing and latches this value. This issue has only been observed recently with newer devices
hat either drive DM high or show excessive ringing during the initial connection, hence causing the speed
detection to be seen as low speed by the TUSB2046B (TUSB2077A, TUSB2036). Note that this device is
used extensively in the USB1.1 Goldtree suite, and this issue was never revealed, further pointing to the
act that some newer devices have less control on DM than previous devices, although this is allowed by
he USB specification. TI has no planned fix in the pipeline, but wants users to be aware of this issue,
which can easily be avoided by guaranteeing that DP be asserted high before DM. In the event that a
alse low speed detection is observed, the situation can be resolved by performing a
CLEAR_PORT_FEATURE(PORT_ENABLE) followed by a RESET_PORT in the software driver,
assuming both DP and DM are now stable.
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