SH7721 datasheet(863/1524 Pages) RENESAS

863 / 1524 page

Section 24

USB Host Controller (USBH)

Rev. 3.00 Jan. 18, 2008 Page 801 of 1458

REJ09B0033-0300

24.7

Usage Notes

1. When using the USB host controller, the bus clock (B

φ) must be set to 32 MHz or higher. The

peripheral clock (P

φ) must also be set to a higher frequency than 13 MHz.

2. Usage notes on Resume operation

(1) Phenomenon

While the USB host is providing an output of a Resume (*1) signal, suppose that (a)

PortPower is turned off or that (b) OverCurrent is produced. In this case, the Resume signal

should ordinarily be stopped so that the idle (*2) state will be established. Actually,

however, the result is that an idle signal is output.

*1: In FullSpeed, D+ = Low and D- = High. In LowSpeed, D+ = High and D- = Low.

*2: In FullSpeed, D+ = High and D- = Low. In LowSpeed, D+ = Low and D- = High.

(2) Conditions when the above phenomenon occurs

While a Resume (*1) signal is being output, (a) PortPower is turned off or (b) OverCurrent

is produced.

(3) Conditions when the above phenomenon does not occur

The above phenomenon will not occur if there is no Resume operation, that is, Suspend

operation has not been done.

(4) Problem avoidance by software

If the above phenomenon occurs, Resume is interrupted and then an idle signal is output.

However, turning on PortPower enables device recognition. The above phenomenon is

removed by the subsequent Port Reset for the device. Normal operation is thus recovered.

Note, however, the above phenomenon will not be removed by USB Reset, which is

generated by the HCFS1 and HCFS0 bits in the Hc Control (USBHC) register. For this

reason, if you are using software that issues USB Reset by the HCFS1 and HCFS0 bits in

the Hc Control (USBHC) register, modify the software so that it issues USB Reset (Port

Reset) by setting the PRS bit in the Hc Rh Port Status 1 or Hc Rh Port Status 2

(USBHRPS1 or USBHRPS2) register.

However, there is no need to take corrective action if Port Rest has already been issued by

the PRS bit before the recognition of USB device connection.

SH7721 Datasheet(PDF) 863 Page - Renesas Technology Corp