Hi Segher, Going from a hypothetical 625 line NTSC to 625 line SECAM (or 525 line NTSC to a hypothetical 525 line SECAM) would not have required a glass delay line. It's a component which is required to decode PAL properly. I found a picture of one opened up. It's an ultrasonic device which relies on the speed of propagation of pressure waves through a medium (in fact quartz). http://www.flickr.com/photos/anachrocomputer/2840365262/ But the hard part remains providing an accurate FM carrier (or pair of carriers). Procep's circuit carries out frequency modulation entirely in the analogue domain. The colour difference signals R-Y and B-Y are available in analogue form after PAL decoding (including cancellation of phase errors using the quartz delay line). These are used to modulate FM carrier oscillators. By the look of the Procep board, there are two oscillators, one for R-Y and one for B-Y, and a switch selects which output forms the SECAM chrominance signal every line. By contrast, Atari's FGTIA circuit is a hybrid of digital and analogue techniques. The FGTIA chip controls a single external FM carrier oscillator, using three bits for colour information. Within that three bit encoding is the information to distinguish the R-Y lines from the B-Y lines. The datasheet acknowledges that the resulting R-Y and B-Y carriers will not be exactly compliant to SECAM spec; fortunately SECAM televisions themselves are quite forgiving as to the exact R-Y and B-Y centre frequencies. Richard -------------------------------------------------- From: "Segher Boessenkool" <email@example.com> Sent: Wednesday, November 02, 2011 8:58 PM To: <firstname.lastname@example.org> Subject: Re: Procep SECAM Re: C16/Plus4 > Hi Richard, > >> You needed glass delay lines to decode PAL or SECAM, not to encode them. > > [snip] > > Ah. So it would have been much simpler for your vic->secam external > circuit if the VIC did not do the PAL alternating thing? They could > have done a chip like that easily. Or do you still need a lot of > conversion circuitry that way? > > > Segher > > > Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing listReceived on 2011-11-03 12:00:03
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