8x931AA, 8x931HA USB PERIPHERAL CONTROLLER
condition can be seen on the oscilloscopes as
excessive overshoot and undershoot. This condition
can potentially introduce bit errors.
6.0 THERMAL CHARACTERISTICS
The microcontroller operates over the commercial
temperature range from 0oC to 70oC. All thermal
impedance data (see Table 17) is approximate for
static air conditions at 1 watt of power dissipation.
Values change depending on operating conditions
and application requirements. The Intel Packaging
Handbook (order number 240800) describes Intel’s
thermal impedance test methodology. The
Components Quality and Reliability Handbook
(order number 210997) provides quality and
reliability information.
7.4 Pullup Resistor Requirement
for 8x931AA/HA devices
The USB specification requires a pullup resistor to
allow the host to identify which devices are low
speed and which are full speed in order to commu-
nicate at the appropriate data rate. For 8x931HA
hub devices (12 Mbps), use a 1.5KΩ pullup resistor
(to 3.0 V – 3.6 V; may use the ECAP pin.) on the
DP0 line. 8x931AA devices can be either full speed
or low speed; add a 1.5KΩ pullup to the appropriate
USB line.
Table 17. Thermal Characteristics
†
†
Package Type
θJA
N/A
θJC
N/A
68-pin PLCC
†
Data unavailable at time of publication.
7.5 Powerdown Mode Cannot Be
Invoked Before USB Suspend
7.0 DESIGN CONSIDERATIONS
7.1 Low Clock Mode Frequency
If the 8x931AA/HA is put into powerdown mode
before receiving a USB suspend signal from the
host, then a USB resume will not properly wake up
the 8x931AA/HA from powerdown mode.
During low clock mode, the internal clock FCLK
distributed to the CPU and peripherals is 3 MHz.
Peripheral timing and external bus accesses
(including instruction fetch and data read/write) are
affected. Refer to Table 10 and Table 11 for clock
rates.
7.6 Unused Downstream Ports
If the USB downstream ports are not used, it is still
required that the two data lines be pulled low
externally (similar to a disconnect) so that the inputs
are not floating. This will eliminate the possibility of
induced system noise. All USB data lines require
15KΩ external pulldown resistors. Do not leave
unused port(s) disconnected.
7.2 Setting RXFFRC Bit Clears Only
the Oldest Packet in the FIFO
If the receive FIFO is set as a dual packet mode,
then it can receive two packets. Setting RXFFRC (in
RXCON registers) to indicate FIFO Read Complete
will not flush the entire FIFO; it will flush only the
oldest packet. The read marker will be advanced to
the location of the read pointer.
7.7 ECAP Usage to Supply 3.0 to 3.6
Volts for 1.5K Ohm Pullup
For a self-powered or bus-powered device, when
the voltage at the VCC pins are at 5.25v, the voltage
at ECAP pin will be at approximately 3.6v. If the VCC
pin is at 4.65v [Min, Vbus Powered (host or hub)
Port specification], the voltage at the ECAP pin will
be at approximately 3.2v (refer to Table 18 below).
The capability for this pin to supply the 3.0v to 3.6v
voltage to the 1.5KΩ USB pullup terminator
depends upon the VCC voltage level.
7.3 Series Resistor Requirement for
Impedance Matching
Per USB rev. 1.0 specification (page 111, section
7.1.1.1), the impedance of the differential driver
must be between 29Ω and 44Ω. To match the cable
impedance, a series resistor of 27Ω to 33Ω should
be connected to each USB line; i.e., on DP0 and on
D
M0. If the USB line is improperly terminated or not
matched, then signal fidelity will suffer. This
24
ADVANCE INFORMATION
