326
AMD Geode™ SC3200 Processor Data Book
Video Processor Module
32581C
7.2.5
Integrated PLL
The integrated PLL can generate frequencies up to 135
MHz from a single 27 MHz source. The clock frequency is
programmable using two registers. Figure 7-14 shows the
block diagram of the Video Processor integrated PLL.
F
REF
is 27 MHz, generated by an external crystal and an
integrated oscillator. F
OUT
is calculated from:
F
OUT
= (m + 1) / (n+ 1) x F
REF
The integrated PLL can generate any frequency by writing
into the “m” and “n” bit fields (FBAR0+Memory Offset 2Ch,
m = bits [14:8] and n = bits [3:0]). Additionally, 16 prepro-
grammed VGA frequencies can be selected via the PLL
Clock Select register (Memory Offset
2Ch[19:16]), if the crystal oscillator has a frequency of 27
MHz. This PLL can be powered down via the Miscella-
neous register (Memory Offset 28h[12]).
Figure 7-14. PLL Block Diagram
F
REF
F
OUT
n
Phase
Charge
m
VCO
Compare
Divider
Divider
Pump
Loop
Filter
Out
Divide
Summary of Contents for Geode SC3200
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Page 350: ...350 AMD Geode SC3200 Processor Data Book Debugging and Monitoring 32581C...
Page 420: ...420 AMD Geode SC3200 Processor Data Book Electrical Specifications 32581C...