Table 13-54. Usbpllctl Register; Table 13-55. Usbpllctl Fields; Usb Pll Control Register (Usbpllctl) - Sharp LH79524 User Manual

Reset, Clock, and Power Controller

13.2.2.23 USB PLL Control Register (USBPLLCTL)

This register controls the USB PLL frequency and power down. The USB PLL frequency
is calculated by:
USBPLLFrequency
The maximum USB PLL frequency is 304.819 MHz
Since the jitter is better with the PLL running above 100 MHz, it is best to program the PLL
to a frequency greater than 100 MHz and divide it by four using the USBPRE:USBDIV bit.
Here is a programming example using the typical crystal frequency of 11.2896 MHz:
Target frequency (48 MHz)
Program USBLOOPDIV = 17 and USBPREDIV = 1
47.9808 ÷ 48.000 MHz = 0.04% Well within USB 2.0 Specification of ±0.25%
192 MHz = (11.2896 MHz × USLOOPDIV) ÷ USBPREDIV
192 MHz ÷ 11.2896 MHz = USBLOOPDIV ÷ USBPREDIV = 17.0068
(11.2896 MHz ÷ 17)/1 = 191.9232 MHz
191.9232 MHz/(USBDIV = 4) = 47.9808 MHz
BIT
FIELD
RESET
RW
BIT
FIELD
RESET
RW
ADDR
BITS
31:14
13
12
11:6
5:0
13-34
(
⎛ SystemClockOscillatorFrequency
-------------------------------------------------------------------------------------------------------------------------------------------------------- -
=
⎝
×

Table 13-54. USBPLLCTL Register

31 30 29 28
0 0 0 0
RO RO RO RO RO
15 14 13 12
///
0 0 1 0
RO RO RW RW RW

Table 13-55. USBPLLCTL Fields

NAME
/// Reserved Writing to these bits has no effect. Reading returns 0.
USB PLL Power Down
USBPDN
1 = USB PLL Active
0 = USB PLL Powered Down
USB PLL Output Frequency Range Select
USBFRANGE
1 = 100 MHz - 304.819 MHz (best jitter performance achieved)
0 = 20 MHz - 100 MHz
USB PLL Pre-Divider Prescales the USB PLL Reference clock. The divisor
USBPREDIV chosen must satisfy the equation:
(System Clock Oscillator frequency)
USB PLL Loop-Divider Prescales the USB PLL Feedback clock. The divisor can
USBLOOPDIV
be programmed from 1 to 63.
USBPREDIV
.
4 = 192 MHz
27 26 25 24 23
///
0 0 0 0 0
RO RO RO RO
11 10 9 8 7
USBPREDIV
0 0 0 0 0
RW RW RW RW
0xFFFE2000 + 0xC4
DESCRIPTION
÷
Version 1.0
LH79524/LH79525 User's Guide
) ×
USBLOOPDIV ⎞
⎠
22 21 20 19
0 0 0 0
RO RO RO RO
6 5 4 3
USBLOOPDIV
1 0 0 0
RW RW RW RW RW
(USBPREDIV) ≥ 5 MHz
18 17 16
0 0 0
RO RO RO
2 1 0
1 0 1
RW RW