LSI Logic Confidential
Clock and Power Registers
16-5
Copyright © 2001, 2002 by LSI Logic Corporation. All rights reserved.
ClkO Src
6
If clear, then the clkO/DAC pin is driven by the output of
the internal adjustable crystal oscillator to provide a
system clock reference. If set, the clkO/DAC pin is driven
by the BIO sigma/delta DAC as specified by the TCdacCtl
register to control an external VCXO. This bit is reset to
zero.
CkISrc27
5
If set, the clock input pin (CLKI) is divided by two before
being applied to the PLLs, PTS and transport stream time
stamp counters. This bit should be set if the external
clock input or crystal frequency is 27 MHz, otherwise it is
assumed to be 13.5 MHz. The 13.5 MHz clock is divided
by 150 before being accumulated in the video PTS
counter register. This bit is reset to one.
The internal clock operating frequency is determined by
N and P as follows
:
SysclkPLL(N) is determined by the table below.
After reset, N is set to 4 and P is set to 1. Software must
change N and P to correct values after reset. Changing
the internal clock frequency will cause DRAM timing
violations particularly when increasing the frequency.
Before changing the internal clock frequency, SDRAM
activity must be stopped by setting the SDRAM stop bit
and reading it until it reads as one. DRAM activity
including cache misses and DMA transfers should be
avoided until the DLLs are reset. The resetDLL bit is a
N
SysclkPLL (Mhz)
0
108
1
121.5
2
135
3
148.5
4
162
5
175.5
6
189
7
202.5
internalClock
SysclkPLL N
( )
P
1
+
----------------------------------------
=