Bootstrap initialization – Digi NS9750 User 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