Both methods (CV/Gate sync and 14-pin sync) are valid and have been supported by LZX since the beginning, so I guess Phil decided he preferred the CV/Gate sync method for the Clock VCO. With the Cadet series, the boards are designed to be multi-purpose, so I wanted the pads of the pin header available for wiring, even if the 14-pin sync wasn’t populated.
14-pin sync in general is a bit of a hassle for our production modules, going with the single RCA sync/genlock input is easier and is also an established standard in the broadcast world – but the extra circuitry it requires in some cases is outside the scope of a DIY module build, where parts count needs to be low, so that’s why we’re using the 14-pin sync in Cadets.
Thanks for the clear explanation Lars!
I was wondering about that RCA sync cable;
I did not know how that worked / how to fit all data (H-sync/V-sync/C-sync/Blanking/Burst/Odd-Even) in a RCA connector.
Most of the time it is the H&V sync , I presume.
but then in a encoded stream, instead of dedicated pins.
Take a look at the LM1881 datasheet. This won’t give you everything on the 14-pin sync header, but if you need to extract hsync and vsync for oscillator syncing, for example, this is a pretty easy way to do it!
So, the RCA sync… are LZX modules that pass sync in this configuration sending “composite-sync” signals (like those that come out of the LM1881)… or a full composite video signal… or something else? I ask because if I wanted to DIY an LZX-compatible module that utilized incoming sync on the RCA, would I need an LM1881 to digest the LZX sync prior to separating H & V sync signals? Or can I skip the LM1881 and just logic the sync signals apart?
@drumasaurusrex It is composite sync driven at video amplitudes 0.6Vpp thru 75R resistor, buffered with video opamp. So you should use LM1881, or if you’re feeling thrifty you could design a sync tip clamp (budget DC restore) circuit and drive that into a comparator. LM1881 is much easier.