2009年4月9日 星期四

[USB] Chirp K/J is different from State K/J

The differential voltage (D+ - D-):
350 ≤ (High-speed J) ≤ 450 < 700 ≤ (Chirp J) ≤ 1100
-900 ≤ (Chirp K) ≤ -500 < -450 ≤ (High-speed K) ≤ -350

The voltage level of state J/K and Chirp J/K is totally in different level, i.e. using state J/K of test mode to simulate chirp is impossible.


USB spec r2.0
p169
  • Test mode Test_J: Upon command, a port’s transceiver must enter the high-speed J state and remain in that state until the exit action is taken. This enables the testing of the high output drive level on the D+ line.
  • Test mode Test_K: Upon command, a port’s transceiver must enter the high-speed K state and remain in that state until the exit action is taken. This enables the testing of the high output drive level on the D- line.

p179


p146

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