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skiselev / omega

Omega Home Computer
GNU General Public License v3.0
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Make Ys available on the RGB connector #39

Open sdsnatcher opened 2 years ago

sdsnatcher commented 2 years ago

Please add the Ys signal to the RGB connector. The pin-5 of the DIN-8 MSX RGB connector was meant to be the Ys signal from the VDP.

To save some pennies on a transistor, many MSX models came with just a resistor divider connected to that pin.

But for those on the SCART world, it's very useful to have a funcional Ys pin, since the TV can superimpose the MSX image over other sources.

I attached here a screenshot of how it was implemented on the Philips NMS-8245.

Philips-NMS-8245_Ys_pin
sdsnatcher commented 2 years ago

There are a lot of free inverters on the current Omega schematic, and any of them could also be used to implement the Ys signal too:

Ys_pin_on_Omega_proposal
skiselev commented 2 years ago

Thanks for the suggestion! I'll add it to the next revision.

Leshak-pcb commented 1 year ago

There are a lot of free inverters on the current Omega schematic, and any of them could also be used to implement the Ys signal too:

Ys_pin_on_Omega_proposal

Since Ys is terminated with 75 Omh resistance this is probably too much for 74HCT04. Increasing series to 150 Omh results in 18.7 mA current - pretty high, but acceptable for 74HCT. 74ACT04 can source up to 24 mA, but is it suitable for a clock generator?