mc68hc908jb8 Freescale Semiconductor, Inc, mc68hc908jb8 Datasheet - Page 132

• Manufacturer Part Number: mc68hc908jb8
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Universal Serial Bus Module (USB)
9.5.5 Low-Speed Device
9.6 Clock Requirements
Technical Data
132
Low-speed devices are configured by the position of a pull-up resistor on
the USB D– pin of the MCU. Low-speed devices are terminated as
shown in
For low-speed transmissions, the transmitter’s EOP width must be
between 1.25 s and 1.50 s. These ranges include timing variations due
to differential buffer delay and rise/fall time mismatches and to noise and
other random effects. A low-speed receiver must accept a 670ns SE0
followed by a J transition as a valid EOP. An SE0 shorter than
330ns or an SE0 not followed by a J transition are rejected as an EOP.
Any SE0 that is 8 s or longer is automatically a reset.
The low-speed data rate is nominally 1.5 Mbps. The OSCXCLK signal
driven by the oscillator circuits is the clock source for the USB module
and requires that a 6-MHz oscillator circuit be connected to the OSC1
and OSC2 pins. The permitted frequency tolerance for low-speed
functions is approximately 1.5% (15,000 ppm). This tolerance includes
inaccuracies from all sources: initial frequency accuracy, crystal
capacitive loading, supply voltage on the oscillator, temperature, and
aging. The jitter in the low-speed data rate must be less than 10ns.
Figure 9-9. External Low-Speed Device Configuration
Universal Serial Bus Module (USB)
Figure 9-9
MCU
MC68HC908JB8•MC68HC08JB8•MC68HC08JT8 — Rev. 2.3
with the pull-up on the D– line.
V
D+
D–
REG
(3.3V)
1.5 k
USB LOW-SPEED CABLE
Freescale Semiconductor