Intel PXA255 3.3.4 95.85 MHz Peripheral Phase Locked Loop, 3.3.5 147.46 MHz Peripheral Phase Locked Loop

Intel® PXA255 Processor Developer’s Manual 3-5
Clocks and Power Manager
3.3.4 95.85 MHz Peripheral Phase Locked Loop
The 95.85MHz PLL is the clock source for many of the peripheral blocks’ external interfaces.
These interfaces require ~48MHz (UDC/USB, FICP), ~33MHz (I2C), and ~20 MHz (MMC). The
generated frequency is not exactly the required frequency due to the chosen crystal and the lack of
a perfect Least Common Multiple between the units. The chosen frequencies keep each unit’s clock
frequency within the unit’s clock to le rance. If a crystal other than 3.6864MHz is used, the clock
frequencies to the peripheral blocks’ inte rfaces may not yield the desired baud rates (or protoco l ’s
rate).
3.3.5 147.46 MHz Peripheral Phase Locked Loop
The 147.46MHz PLL is the clock source for many of the peripheral blocks’ external interfaces.
These interfaces require ~14.75MHz (UARTs), 12.288MH z (AC97), and variable frequencies
(I2S). The generated frequency may not exactly match the required frequency due to the choice of
crystal and the lack of a perfect Least Common Multiple between the un its. The cho sen fr equencies
keep each unit’s clock frequency within the unit’s clock tolerance. If a crystal other than
3.6864MHz is used, the clock frequencies to the peripheral blocks’ interfaces may not yield the
desired baud rates (or other protocol’s rate)
Table 3-1. Core PLL Output Frequencies for 3.6864 MHz Crystal
LM
Turbo Mode Frequency (MHz) for Values
“N” and Core Clock
Configuration Register (CCCR[15:0])
programming for Values of “N” PXbus
Frequency
(MHz)
MEM, LCD
Frequency
(MHz)
SDRAM
max
Frequency
(MHz)
1.00
(Run) 1.50 2.00 3.00
27 1 99.5
@1.0V —199.1 @1.0V 298.6 @1.1V 50 99.5 99.5
36 1 132.7
@1.0V — — — 66 132.7 66
27 2 199.1
@1.0V 298.6 @1.1V 398.1 @1.3V — 99.5 99.5 99.5
36 2 265.4
@1.1V — — — 132.7 132.7 66
45 2 331.8
@1.3V — — — 165.9 165.9 83
27 4 398.1
@1.3V — — — 196 99.5 99.5
Table 3-2. 95.85 MHz Peripheral PLL Output Frequencies for 3.6864 MHz Crystal
Unit Name Nominal Frequency Actual Frequency
USB (UDC) 48M Hz 47.923 M Hz
FICP 48M Hz 47.923MHz
I2C 33MHz 31.949MHz
MMC 20MHz 19.169MHz