Precautions For Usb - Renesas M16C Series User Manual

M30245 Group

2.8.9 Precautions for USB

(1) USB Communication
"In applications requiring high-reliability, we recommend providing the system with protective mea-
sures such as USB function initialization by software or USB reset by the host to prevent USB com-
munication from being terminated unexpectedly, for example due to external causes such as noise."
(2) Peripheral Circuit
The peripheral circuit block diagram is shown in Figure 2.8.51, the passive part of LPF pin is shown in
Figure 2.8.52 and the connection diagram of decoupling capacitor is shown in Figure 2.8.53.
•USB2.0 specification specifies the driver impedance 28~44Ω (See 7.1.1.1 "Full-speed (12Mb/s)
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Driver Characteristics"). Connect a serial resistor (recommended value: 27~33Ω) to the USB D+ pin
and the USB D- pin to satisfy this specification. Also connect, if required, the capacitors between the
USB D+ pin/USB D- pin and the Vss pin. These capacitors control ringing or adjust the times of
rising/falling and the crossover point of D+/D-. As the numerical values and the configuration of the
peripheral components need to be adjusted according to differences in characteristic impedance and
layout of the mount printed circuit board. Therefore, fully evaluate on the system in use and observe
waveforms before adjusting the connection or disconnection and the values of the resistance and the
capacitor.
•When the USB Attach/Detach function is not used, connect the UVcc pin and the USB D+ pin via a
1.5kΩ resistance (D+ line pull-up timing depends on the UV
When the USB Attach/Detach function is used, connect the P9
a 1.5kΩ resistance. Irrespective of use of the USB Attach/Detach function, connect the UV
the power supply. In addition, the time required for the host PC to recognize the USB Attach/Detach
varies depending on the whole system state such as substrate resistance components, capacitance
components, USB cable capacitance, and substrate characteristics and processing speed of the
host. Fully evaluate on the system subject to actual use.
•Connect all the passive parts of the LPF pin as close to the LPF pin as possible.
•Connect an insulating connector (ferrite beads) between the AVss pin and the digital Vss, between
the AVcc pin and the digital Vcc. Also at this time, when an A/D converter is used, connect the Vref
pin to the AVcc pin.
Rev.2.00 Oct 16, 2006
REJ09B0340-0200
page 210 of 354
pin).
CC
/ATTACH pin and the USB D+ pin via
0
2. USB function
pin to
CC