Datasheet

Universal Serial Bus Module (USB)
Technical Data MC68HC908JB8•MC68HC08JB8•MC68HC08JT8 — Rev. 2.3
136 Universal Serial Bus Module (USB) Freescale Semiconductor
Figure 9-13. Data Jitter
For low-speed transmissions, the jitter time for any consecutive
differential data transitions must be within
±25ns and within ±10ns for
any set of paired differential data transitions. These jitter numbers
include timing variations due to differential buffer delay, rise/fall time
mismatches, internal clock source jitter, noise and other random effects.
9.7.2.5 Data Signal Rise and Fall Time
The output rise time and fall time are measured between 10% and 90%
of the signal. Edge transition time for the rising and falling edges of
low-speed signals is 75ns (minimum) into a capacitive load (C
L
) of
200pF and 300ns (maximum) into a capacitive load of 600pF. The rising
and falling edges should be transitioning (monotonic) smoothly when
driving the cable to avoid excessive EMI.
Figure 9-14. Data Signal Rise and Fall Time
CONSECUTIVE
TRANSITIONS
t
Period
DIFFERENTIAL
DATA LINES
CROSSOVER
POINTS
PAIRED
TRANSITIONS
JITTER
t
R
DIFFERENTIAL
DATA LINES
t
F
RISE TIME
FALL TIME
10%
90%
90%
10%
LOW SPEED: 75ns at C
L
= 200pF, 300ns at C
L
= 600 pF
C
L
C
L
+
+