Digi NS9750 - Manual (Page 296)

S y s t e m a t t r i b u t e s
2 7 2 N S 9 7 5 0 H a r d w a r e R e f e r e n c e
Figure 62 shows how the PLL clock is used to provide the NS9750 system clocks.
Figure 62: NS9750 system clock generation (PLL)
Bootstrap initialization
The PLL and other system configuration settings can be configured at powerup before
the CPU boots. External pins are used to configure the necessary control register bits
at powerup. External pulldown resistors can be used to configure the PLL and system
configuration registers depending on the application. The recommended value is 2.2k
ohm to 2.4k ohm.
PLL
FN
FBM
FS[1:0]
ND[4:0]
CKOUT = 796.2624 MHz
FBM = 398.1312 MHz
divider = FS = 2
multiplier = ND + 1 = 27
CN
set by
strapping
OSC
20MHz -
40MHz
BP
Note, to use an external
oscillator, place a 100 ohm
resistor in series between
the oscillator and x1
29.
491
2 M
H
z
x1_sys_osc
x2_sys_osc
div by
2
fixed
div by
4
fixed
div by 8
fixed
cpu_clock (199.0656 MHz)
ahb_clock (99.5328 MHz)
bbus_clock (49.7664 MHz)
div by
14, 12, 10 or 8
fixed by strapping
div by
4, 8, 16, or 32
configurable
lcd_clock
(internal or external source)
lcd_clock_control (configurable)
pci_clk_control (configurable)
pci_clock_out
main clocks
to modules
pci_clock (28.4379 MHz)
lcdclock
pci_clock_in
pci_clk
CKOUT
MUL by
ND (27)
DIV by FS
(2)
Sample Clock Frequency Settings With 29.4912MHz Crystal (FS= 01, div by 2)
ND+1 f
VCO
cpu_clk hclk bbus_clk pci_clk lcd_clk
27 398.1312 199.0656 99.5328 49.7664 28.4379(14) 99.5328 - 12.4416
26 383.3856 191.6928 95.8464 47.9232 31.9488(12) 95.8464 - 11.9808
25 368.6400 184.3200 92.1600 46.0800 30.7200(12) 92.1600 - 11.5200
24 353.8944 176.9472 88.4736 44.2368 29.4912(12) 88.7872 - 11.0592
23 339.1488 169.5744 84.7872 42.3936 28.2624(12) 84.7872 - 10.5984
22 324.4032 162.2016 81.1008 40.5504 32.4403(10) 81.1008 - 10.1376
21 309.6576 154.8288 77.4144 38.7072 30.9657(10) 77.4144 - 9.6768
20 294.9120 147.4560 73.7280 36.8640 29.4912(10) 73.7280 - 9.2160
19 280.1644 140.0832 70.0416 35.0208 28.0164(10) 70.0416 - 8.7552
18 265.4208 132.7104 66.3552 33.1776 26.5420(10) 66.3552 - 8.2944
17 250.6752 125.3376 62.6688 31.3344 31.3344(8) 62.6688 - 7.8336
16 235.9296 117.9648 58.9824 29.4912 29.4912(8) 58.9824 - 7.3728
15 221.1840 110.5920 55.2960 27.6480 27.6480(8) 55.2960 - 6.9120
14 206.4384 103.2192 51.6096 24.8048 25.8048(8) 51.6096 - 6.4512