
NON-DISCLOSURE
AGREEMENT
REQUIRED
Universal Serial Bus Module (USB)
General Release Specification
MC68HC08KL8 — Rev. 2.0
Universal Serial Bus Module (USB)
9.5.3 USB Transceiver
The USB transceiver provides the physical interface to the USB D+ and
D– data lines. The transceiver is composed of two parts: an output drive
circuit and a receiver.
9.5.3.1 Output Driver Characteristics
The USB transceiver uses a differential output driver to drive the USB
data signal onto the USB cable. The static output swing of the driver in
its low state is below the VOL of 0.3 V with a 1.5-k load to 3.6 V and in
its high state is above the VOH of 2.8 V with a 15-k load to ground. The
output swings between the differential high and low state are well
balanced to minimize signal skew. Slew rate control on the driver is used
to minimize the radiated noise and cross talk. The driver’s outputs
support 3-state operation to achieve bidirectional half duplex operation.
The driver can tolerate a voltage on the signal pins of –0.5 V to 3.8 V with
respect to local ground reference without damage.
9.5.3.2 Low Speed (1.5 Mbs) Driver Characteristics
The rise and fall time of the signals on this cable are greater than 75 ns
to keep RFI (radio frequency interference) emissions under FCC
(Federal Communications Commission) class B limits and less than
300 ns to limit timing delays, signaling skews, and distortions. The driver
reaches the specified static signal levels with smooth rise and fall times
and minimal reflections and ringing when driving the cable. This driver is
used only on network segments between low-speed devices and the
ports to which they are connected.
USB data transmission is done with differential signals. A differential
input receiver is used to accept the USB data signal. A differential 1 on
the bus is represented by D+ being at least 200 mV more positive than
D– as seen at the receiver, and a differential 0 is represented by D–
being at least 200 mV more positive than D+ as seen at the receiver. The
signal crossover point must be between 1.3 V and 2.0 V.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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