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[ADV7391] PAL Output

Question asked by ctb on Mar 26, 2015
Latest reply on Jul 14, 2016 by MathiasBuder

Hello,

 

I'm trying to generate a PAL SD signal using the ADV7391. The input comes from a camera in BT.601/656 format. I'm using only one DAC (register 0x00 = 0x10) in CVBS mode (reg 0x82 = 0xC3). So I'm expecting a signal according to the BT.470 standard (other registers: 0x80 = 0x11, 0x8C-0x8F according to frequency).

 

When generating the color bars test pattern everything works fine and the signal looks like BT.470. But when using the camera signal, the output signal is not correct. The time between the EAV and SAV signals according to BT.470 is 12 µs, the line-blanking interval. This consists of 1.5 µs front porch, 4.7 µs sync signal and 5.7 µs back porch. The ADV7391 starts the sync signal immediately when receiving the EAV signal and it's 7.5 µs long instead of 4.7 µs. So the front porch is fully missing and the back porch is too short. The color burst starts correctly around 0.7µs after the end of the sync pulse.

 

I really tried a lot, but my monitors are always losing the sync. Some monitors do never get a sync. I hope that you have some ideas what's going wrong. How is the timing of front porch/sync/back porch generated?

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