HD6417705 Datasheet, PDF (516/739 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7700 Series

18.8 Example of USB External Circuitry
1. USB Transceiver
A USB transceiver IC (such as a PDIUSBP11) should be connected externally when no
internal transceiver is used. The USB transceiver manufacturer should be consulted concerning
the recommended circuit from the USB transceiver to the USB connector, etc.
2. D+ Pull-Up Control
In a system where it is wished to disable USB host/hub connection notification (D+ pull-up)
(during high-priority processing or initialization processing, for example), D+ pull-up should
be controlled using a general output port. However, if a USB cable is already connected to the
host/hub and D+ pull-up is prohibited, D+ and D– will both go low (both of D+ and D– pulled
down on the host/hub side) and the USB module will mistakenly identify this as reception of a
USB bus reset from the host. Therefore, the D+ pull-up control signal and VBUS pin input
signal should be controlled using a general output port and the USB cable VBUS (AND
circuit) as shown in figure 18.17. (The UDC core in this LSI maintains the powered state when
the VBUS pin is low, regardless of the D+/D– state.)
3. Detection of USB Cable Connection/Disconnection
As USB states, etc., are managed by hardware in this module, a VBUS signal that recognizes
connection/disconnection is necessary. The power supply signal (VBUS) in the USB cable is
used for this purpose. However, if the cable is connected to the USB host/hub when the
function (system installing this LSI) power is off, a voltage (5 V) will be applied from the USB
host/hub. Therefore, an IC (such as an HD74LV1G08A or 2G08A) that allows voltage
application when the system power is off should be connected externally.
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