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ADV7343 CVBS Clock Problem

Question asked by e3e on Apr 15, 2018
Latest reply on Apr 16, 2018 by PoornimaSubramani

Hi all,

 

I'm using Silicon Motion's SM750 GPU and ADV7343 encoder for both VGA and CVBS outputs. SM750 provides 2 VGAs and 24bit flat panel outputs and I'm using 1 VGA and 24bit RGB flat panel output for CVBS.

 

I applied 27MHz signal to ADV7343's Clk_a pin and wrote to registers this values:

0x17   0x02

0x00   0xFC

0x82   0xC9

0x84   0x40

0x80   0x11

 

And colored Sd test patterns worked with PAL outputs. After that I connected SM750's pixel clock output with ADV7343's clk_a pins directly (via 0R resistor). I programmed registers with these table values (Table 81).

I checked the resolution in Windows OS and set resolution 640x480, 60Hz. But there is no video output. I checked frequency of pixel clocks and saw 25.175 MHz. I searched the engineer zone's page and understood there is allways 27 Mhz clock must applied clk_a pin. If I use 800x600, 60Hz resolution, pixel clock will arise 40 Mhz. I'm confused.

I believe my circuit is true but there is an another problem and I can't see. What should i do or which frequency applied to clk_a pin? Is 27 Mhz clock freq. necessary?

 

Thanks for all your reply.

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