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DAC and PLL Programming
4–14
Rev 02; February 8, 2002
4.3 PROGRAMMING EXAMPLE FOR PLL MODE
This example provides detailed calculations for programming the PLL and PWG registers in PLL mode. Either the
“total horizontal line time” or the “active time” is required, and the desired number of pixels in the output; either
active or total. The “total horizontal line time” includes the active, sync, and blank regions. Use the following work-
sheet to calculate the required register settings:
PLL MODE: Format_____________________
Active pixel resolution: H=______ x V=______
Total pixel resolution: H=______ x V=______
1.
Determine desired Clock Rate (in us) using one of the following formulas (both give the same result):
Pclk = (Total horizontal line time / total number of pixels desired)
or
Pclk = (Active line time / Active number of pixels)
Pclk = ________ / _________ = _________ (time in us)
Fdesired = 1 / Pclk = ________ (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 = 230 MHz / ______ = ______
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 = ______
LCOUNT has two register settings for 4 and two settings for 8; use either setting.
3.
Calculate the VCO gain using the following formulas:
First find the Fvco using PDA, LCOUNT and Fdesired:
Fvco = PDA x LCOUNT x Fdesired
Fvco = _____ x _____ x _____ = ______
Use Fvco to find VCO Gain:
VCO Gain = Fvco / 3.5Volts
VCO Gain = _____ / 3.5Volts = _______ 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). If the calculated gain is 12, use the next highest value for VCO of 15, not 10.
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