MC908JB16DWE Datasheet, PDF (177/332 Pages) Freescale Semiconductor, Inc – Microcontrollers

Universal Serial Bus Module (USB)
11.7 Hardware Description
The USB module as previously shown in Figure 11-2 contains three
functional blocks: the low-speed USB transceiver, the USB control logic,
and the USB registers. The following details the function of the regulator,
transceiver, and control logic. See 11.8 I/O Registers for details of
register settings.
11.7.1 Voltage Regulator
The USB data lines are required by the USB specification to have an
output voltage between 2.8V and 3.6V. The data lines also are required
to have an external 1.5kΩ pull-up resistor connected between a data line
and a voltage source between 3.0V and 3.6V. Figure 11-10 shows the
worst case electrical connection for the voltage regulator.
4.0V TO 5.5V
3.3 V
REGULATOR
LOW-SPEED
D+
TRANSCEIVER
D–
USB DATA LINES
R1
USB CABLE
R1 = 1.5kΩ ±5%
R2 = 15kΩ ±5%
R2 R2
HOST
OR
HUB
Figure 11-10. Regulator Electrical Connections
11.7.2 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.
MC68HC908JB16 — Rev. 1.1
Freescale Semiconductor
Universal Serial Bus Module (USB)
Technical Data
177