M68HC08 datasheet(178/332 Pages) FREESCALE

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Universal Serial Bus Module (USB)

Technical Data

MC68HC908JB16 — Rev. 1.1

178

Universal Serial Bus Module (USB)

Freescale Semiconductor

11.7.2.1 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 0.3V with a 1.5kΩ load to 3.6V and in

its high state is above the VOH of 2.8V with a 15kΩ 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 –1.0V to 5.5V with

respect to local ground reference without damage.

11.7.2.2 Low Speed (1.5 Mbps) Driver Characteristics

The rise and fall time of the signals on this cable are greater than 75ns

and less than 300ns. The edges are matched to within

±20% to minimize

RFI emissions and signal skew.

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 200mV more positive than

D– as seen at the receiver, and a differential 0 is represented by D–

being at least 200mV more positive than D+ as seen at the receiver. The

signal cross over point must be between 1.3V and 2.0V.

Figure 11-11. Receiver Characteristics

ONE BIT

TIME

(1.5 Mb/s)

SIGNAL PINS

PASS OUTPUT SPEC

LEVELS WITH MINIMAL

REFLECTIONS AND RINGING

VSE (min.)

VSE (max)

VSS

M68HC08 Datasheet(PDF) 178 Page - Freescale Semiconductor, Inc