402-00005-00
DAC and PLL Programming
4–18
Rev 02; February 8, 2002
4.4 PROGRAMMING EXAMPLE FOR XTAL MODE
This example provides detailed calculations for programming the PLL and PWG registers in XTAL mode. The for-
mulas are only slightly different from the ones used for PLL mode. The total horizontal line time or active time is
required as well as the desired number of output pixels, either active or total. Use the following worksheet to calcu-
late the required register settings:
XTAL MODE: Format_____________________
Active pixel resolution: H=______ x V=______
Total pixel resolution: H=______ x V=______
1.
Determine desired Clock Rate (in ns) using one of the following formulas (both give the same result):
Pclk-d = (Total horizontal line time / total number of pixels desired)
or
Pclk-d = (Active line time / Active number of pixels)
Pclk-d = ________ / _________ = _________ (time in us)
Fdesired = 1 / Pclk-d = _______ (frequency in MHz)
For RS-170: the total line time is 63.556 us and the Active time is 52.656 us
For CCIR: the total line time is 64 us and the Active time is 51.95 us
2.
Determine PDA and LCOUNT:
Let ODA (Output Divider Actual) = PDA x LCOUNT
Find ODD (Output Divider Desired) using the following formula:
ODD = 230MHz / Fdesired
ODD = 230MHz / ______ = ______
Use the four tables at the end of this chapter to find a combined value of PDA and LCOUNT which comes closest to
ODD; however, ODA
ODD, or (PDA x LCOUNT)
ODD
Selected PDA = ______
Selected LCOUNT = ______
3.
Calculate the VCO Gain using the following formulas:
First find the Fvco using PDA, LCOUNT and Fdesired:
Fvco-1 = PDA x LCOUNT x Fdesired
Fvco-1 = _____ x _____ x _____ = ______
Use Fvco-1 to find VCO Gain:
VCO Gain = Fvco-1 / 3.5Volts
VCO Gain = _____ / 3.5 Volts = _______ MHz/Volt
Program the VCO bits to the value which is equal to or greater than the value calculated for VCO Gain (see register
definition for VCO bits).
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