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Products => Computers => Vintage Computing => Topic started by: TinkeringSteve on October 24, 2021, 01:07:57 pm

Title: RGB monitor signal generation questions (e.g. Commodore 1084)
Post by: TinkeringSteve on October 24, 2021, 01:07:57 pm
Hello there.

I have a Commodore 1084 monitor now, a 1991 one but it still has RGBi also (for C128 / CGA), not as an extra jack, but switcheable.

Next to using it with retro hardware, I'd also like to tinker around with it (look at my name!).
As in, generate a signal.

I guess I will try the digital RGB one, as it seems simple. But I'd also like to try to generate analog RGB.
I'll list a few things I'm not sure about. (partially pertaining to both, digital and analog RGB)
And perhaps someone cares to point out mistakes or/and answer questions.


Ok, it feels like I forgot some things, but I'll add them latest after I stumbled upon them during attempted implementation ;)
Title: Re: RGB monitor signal generation questions (e.g. Commodore 1084)
Post by: madires on October 24, 2021, 03:16:48 pm
Be aware that there are several slightly different models of the 1084, and the manual usually came with the schematics.

1) 3.3V should work (there are some 74LS at the input)
2) The video IC has a single rail supply and coupling caps at the inputs. So it should be 0 - 0.7V. For the maximum input voltage see the datasheet of the video IC.
3)I don't think the impedance is that important.
4) no idea
5) sync IC's datasheet?
Title: Re: RGB monitor signal generation questions (e.g. Commodore 1084)
Post by: Benta on October 24, 2021, 04:29:18 pm
2: DC level is unimportant, 0.7 Vpp is the specification for RGB
3: It's important, otherwise you risk blurred graphics.
4: HSync pulse length is 4.7 us. VSync is 5 lines.
5: Interlace vs. non-interlace is determined by your VSync. If you keep a constant VSync timing it's non-interlaced. If you shift the VSync pulse back-and-forth by half a line you'll get interlace.

Note that all sync timing is referred to the falling edges of the sync pulses (50% point). The length is not too important.