04-06-2024, 01:13 PM
(This post was last modified: 04-06-2024, 01:15 PM by ppppenguin.)
The PM5544 always had a circle. In the early versions the data for this was in the core. Later versions had a PROM. The data is in the form of pixel counts to the start of the circle on each line. I think it uses 4-fold symmetry to keep the size down.
Many test pattern and testcard generators didn't have a circle as it was too hard or expensive. The PM5519 TV menders' generator has an analogue circle using parabolic waveforms. Obviously not inherently accurate as it has to be adjusted for circularity and centring. I dimly recall a design in CQTV (1980s or 1990s?) that I think used an arrangement of 74LS161 counters to make a circle. I think it was integrating H and V counts to make parabolae. I've done more sophisticated versions of this in FPGAs for some of my SPG/TPG designs.
The PM5544 was designed before most TTL MSI chips such as the 74161 4 bit counter were available. Hence it uses nothing more complex than dual flip-flops and AND/OR/INVERT gates. Except for the text generator which I think was later and uses 74150 16:1 mux chips.
The PAL coder was a separate unit. We don't have the Philips one, but we have plenty of PAL coders so it isn't a problem.
The PM5544 needs mixed sync and mixed blanking. I had to ferret round the back of my apparatus bay to bring the mixed blanking out from my master SPG to a socket on the bench. Not sure I've ever needed a feed of it before. Nor any other "traditional" pulses: burst gate, PAL square wave, line drive, field drive.
Many test pattern and testcard generators didn't have a circle as it was too hard or expensive. The PM5519 TV menders' generator has an analogue circle using parabolic waveforms. Obviously not inherently accurate as it has to be adjusted for circularity and centring. I dimly recall a design in CQTV (1980s or 1990s?) that I think used an arrangement of 74LS161 counters to make a circle. I think it was integrating H and V counts to make parabolae. I've done more sophisticated versions of this in FPGAs for some of my SPG/TPG designs.
The PM5544 was designed before most TTL MSI chips such as the 74161 4 bit counter were available. Hence it uses nothing more complex than dual flip-flops and AND/OR/INVERT gates. Except for the text generator which I think was later and uses 74150 16:1 mux chips.
The PAL coder was a separate unit. We don't have the Philips one, but we have plenty of PAL coders so it isn't a problem.
The PM5544 needs mixed sync and mixed blanking. I had to ferret round the back of my apparatus bay to bring the mixed blanking out from my master SPG to a socket on the bench. Not sure I've ever needed a feed of it before. Nor any other "traditional" pulses: burst gate, PAL square wave, line drive, field drive.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
