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Info needed on mono signal from XT machine

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First post, by zb10948

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Hello,

I have a question regarding Olivetti M19's internal graphics card, that can be set to mono or color mode, depending on the type of screen you originally had. But it was only 2 proprietary monitors supported, both are undocumented as far as schematics go, as their refresh rates are limited the signal is modified to accommodate them and no standard screens can be used.

When set to colour mode, the card outputs TTL values on RGBI pins, with 60Hz refresh and 16.8kHz vsync. Apart from the vsync everything looks like normal colour CGA.

It's the mono mode I'm highly curious about because I can't identify the type of signal attached.
When booted in mono, text mode looks like MDA but it's at a way lower refresh, of 47Hz, which stays the same when you go to CGA graphics modes.

The machine has a single clock of 14.318 coming out from integrated Faraday chipset.

Reply 1 of 3, by BitWrangler

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So I would imagine 47hz would have a chance of synching on a PAL standard monitor. The easy way if you've got a European Amiga monitor with digital/TTL input capability, (5V) is to put it into that and see what happens. Otherwise you'd have to convert it to 1V peak to peak and try it on a PAL composite input... I think.

Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.

Reply 2 of 3, by zb10948

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So this is composite signal?
Very curious because the text mode looks great and crisp.

Reply 3 of 3, by BitWrangler

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Well in as far as mono is basically only luminance info and no color it's similar enough to composite, though appearing to be too high a voltage to put into TVs VCRs etc that expect 1V peak to peak or sometimes given as 0.7V, not sure that's actually lower or the RMS value.

Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.

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