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ADV7401/3 back to back with ADV7342/43 P_BLANK signal?

Question asked by ALaMothe on Jul 2, 2010
Latest reply on Jul 6, 2010 by ALaMothe

The ADV7401 has both an SD and HD decoder inside it, so I don't need to two chips to do SD/HD, considering that I am directly hooking the ADV7401 to the ADV7343 tying together the S_HSYNC, S_VSYNC, with the P_HSYNC, P_VSYNC respectively on the ADV7343 side and feeding them from the ADV7401's HSYNC and VSYNC since I will only use it in SD or HD mode at any time. So far so good.


Thus, if I decide to use external sync signals and not use the embedded EAV/SAV codes I would be covered. But, what should I do with the P_BLANK signal input on the ADV7343, I am not sure why its even necessary, since the encoder should be able to determine everything from HSYNC and VSYNC, but since I am doing a "dev board" like design, I just want to have as much flexibility as possible.


The same reference design (attached) uses two decoders 7403 (HD) and 7180 (SD), but again, P_BLANK is not sourced from anywhere as far as I can tell, its on the bus header, but no source chip is generating it?


As far as I can tell the ADV7401/3 do NOT have a blanking output pin to connect to this, the closest thing is the FIELD/DE pin, but that indicates the field and has nothing to do with the blanking period.


Am I missing something, or should we just tie P_BLANK to 0 on the ADV7342/43? In the datasheet for the ADV7342/43 I can't really find any discussion of the signal other than it in the timing diagrams. But, bottom line is that if I use the ADV7401/03 back to back with the ADV7342/43, I should be able to choose to use external sync signals for HD modes, but since the ADV7342/43 requires P_BLANK? and the ADV7401/03 doesn't output this signal, what should we do?