CX25870/871
1.0 Functional Description
Flicker-Free Video Encoder with Ultrascale Technology
1.3 Device Description
Table 1-14. Adjustment to the PLL_INT and PLL_FRACT Registers
1. What is input frequency to CX25870/871’s CLKI input from data master?
2. Depending on answer to step 1, find an autoconfiguration mode that has a clock frequency close to the
incoming CLKI frequency (within 1 MHz is preferred).
3. Look up the desired clock frequency for the chosen autoconfiguration mode in Appendix C of the
CX25870/871 data sheet.
4. Determine the scaling factor ‘x’ where:
x =
input frequency to CLKI input (usually from data master)
autoconfiguration mode frequency as specified in Appendix C
5. Determine the PLL_INT value in hex by reading back the CX25870/871’s register 0xA0 for that
autoconfiguration mode. This register value can also be found by looking it up in Appendix C.
6. Convert the PLL_INT register value to decimal.
7. Multiply the answer found in step 6 by 216 = 65536.
8. Determine the PLL_FRACT value in hex by reading back the CX25870/871’s register 0x9E and 0x9C.
These two registers cascade to form the PLL_FRACT[15:0] 2-byte value. These register values can
also be found by looking them up in Appendix C.
9. Convert the 2-byte PLL_FRACT register value to decimal.
10. From steps 7 and 9, add the PLL_INT and PLL_FRACT decimal values.
11. Multiply the total found from step 10 by the scaling factor ‘x’ found from step 4.
12. Convert the answer from step 11 to the hexadecimal format. The value should be comprised of a total
of three bytes. The most significant byte will likely be the original PLL_INT[7:0] byte from step 2.
13. Program the bytes determined from step 12 into the CX25870/871’s PLL_INT[7:0] and
PLL_FRACT[15:0] registers. The most significant byte from step 12 is the new PLL_INT value.
Write this to register 0xA0. The 2 least significant bytes from step 12 is the new PLL_FRACT value.
Write these bytes in order to registers 0xBE and 0xBC respectively.
1.3.10 Input Formats
The device can convert a wide range of input formats to analog standard or
HDTV television video formats. The input can be either noninterlaced or
interlaced digital data from 320 x 200 to a maximum of 1024 x 768 pixels per
frame for standard TV outputs. While generating HDTV outputs the device can
accept greater than 1024 x 768 input frames. Many other nonstandard input
formats can be encoded as well. For detailed information on the CCIR601 mode,
please refer to the DVD Movie Playback Architecture and Solutions Application
Note. This application note can be obtained from your local Conexant Systems
sales office.
For instructions on how to display nonstandard resolutions on the TV, request
the “Supporting TV Out with Non-Standard Graphics Input Resolutions”
Application Note from your local Conexant Systems sales office.
100381B
Conexant
1-27
CONEXANT [ CONEXANT SYSTEMS, INC ]
