15-08-2019, 03:11 PM
I think I've cracked the tricky bit. Getting reliable syncs separated from the 405 line input.
H sync is easy enough. The SAA7118 does a good job of this. I've routed it out through an auxiliary pin directly to the FPGA. V sync and odd/even field were much harder. The SAA7118 does a lousy job of these. I couldn't find a way to utilise any pulses from the decoder. Fortunately the ADC's output can be connected directly to the digital video output pins. AGC and black level clamp has already been done in the SAA7118 so I can separate the syncs simply by slicing at a suitable threshold. Then it's pretty much routine logic to separate V sync and odd/even pulses. This now all works.
There's still detailed work to be done. The horizontal alignment has gone wrong. Not a big problem, I'll make it adjustable for now. Also the interpolator is still giving ragged edges. Don't know if it's the interpolator itself or some bad timings.
I am now certain this will work properly.
H sync is easy enough. The SAA7118 does a good job of this. I've routed it out through an auxiliary pin directly to the FPGA. V sync and odd/even field were much harder. The SAA7118 does a lousy job of these. I couldn't find a way to utilise any pulses from the decoder. Fortunately the ADC's output can be connected directly to the digital video output pins. AGC and black level clamp has already been done in the SAA7118 so I can separate the syncs simply by slicing at a suitable threshold. Then it's pretty much routine logic to separate V sync and odd/even pulses. This now all works.
There's still detailed work to be done. The horizontal alignment has gone wrong. Not a big problem, I'll make it adjustable for now. Also the interpolator is still giving ragged edges. Don't know if it's the interpolator itself or some bad timings.
I am now certain this will work properly.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
