HD6417705 Datasheet, PDF (327/739 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7700 Series

9.4.2 USB Clock Frequency Control Register (UCLKCR)
UCLKCR is an 8-bit readable/writable register.
Word-size access is used to write to this register. This writing should be performed with H'A5 in
the upper byte and the write data in the lower byte.
Bit
Initial
Bit
Name
Value R/W
7
USSCS1 1
R/W
6
USSCS0 1
R/W
5
USBEN 1
R/W
4 to 0 
0
R
Description
Source Clock Selection Bit
These bits select the source clock.
00: Clock stopped
01: Setting prohibited
10: Setting prohibited
11: External input clock
USB On-chip Oscillator Enable
This bit controls the operation of the USB on-chip
oscillator.
0: USB on-chip oscillator stopped
1: USB on-chip oscillator operates
Reserved
These bits are always read as 0. The write value
should always be 0.
9.4.3 Usage Notes
Note the following when using the USB. If these are used incorrectly, the correct clocks may not
be generated, causing faulty operation of the USB.
1. UCLKCR is used only for generation of the USB clocks. When the USB is not used, it is
recommended that UCLKCR be cleared to H'00 to halt the clock.
2. Halt the USB before changing the values of UCLKCR. Halt the USB by stopping the clock
supply using the USB module stop bits in STBCR3.
3. UCLKCR is initialized only by a power-on reset. In a manual reset, they retain their current set
values.
4. Use the USB module with Pφ > 13 MHz. Otherwise, the operation of this LSI is not
guaranteed.
Rev. 2.00, 09/03, page 281 of 690