Datasheet

Universal Serial Bus Module (USB)
Hardware Description
MC68HC908JB8•MC68HC08JB8•MC68HC08JT8 — Rev. 2.3 Technical Data
Freescale Semiconductor Universal Serial Bus Module (USB) 133
9.7 Hardware Description
The USB module as previously shown in Figure 9-2 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 9.8 I/O Registers for details of
register settings.
9.7.1 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 9-10 shows the
worst case electrical connection for the voltage regulator.
Figure 9-10. Regulator Electrical Connections
9.7.2 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.
R1
D+
D–
USB CABLE
LOW-SPEED
TRANSCEIVER
R2 R2
HOST
OR
HUB
3.3V
REGULATOR
4.0V – 5.5V
USB DATA LINES
R1 = 1.5kΩ ±5%
R2 = 15kΩ ±5%