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c0pperdragon / A-VideoBoard

FPGA board to create a component video signal for vintage computers.
MIT License
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Atari 5200 #7

Open Icelvlan88 opened 4 years ago

Icelvlan88 commented 4 years ago

Hello,

I see the Atari 5200 Sophia RGB is compatible with Atari 400, not sure if it a different board than the 5200 one. Do you think yours is compatible with 5200?

c0pperdragon commented 4 years ago

I am pretty sure this should work. The 5200 is basically identical to the other machines of the 8-bit series in regards of its video system.

Icelvlan88 commented 4 years ago

Can this board output RGBs? Is it the same as the c64 board or this is something completely different? Preferably TTL sync.

c0pperdragon commented 4 years ago

The A-Video board, when running the Atari firmware, can be jumpered to output RGsB. This may be already anough for you if your monitor can accept RGsB instead of RGB (most do ignore the sync pulses on the G line without problem) and you can additionally use the standard composite video signal as sync source.

If you have more specific demands on your signals, you can also desolder R1 from the FPGA board. This removes the sync signal from the G line and you can instead directly grab the pure sync pulse from the solder pad of R1 located nearer to the FPGA. It is a 3.3V level signal, so it should be compatible with anything that accepts TTL levels.

Icelvlan88 commented 4 years ago

I thought TTL was 5V is there a way to make the voltage higher? also this is a different board than c64 board correct? How would this be installed in 5200?

c0pperdragon commented 4 years ago

Oops - I was mistaken. The Atari mod firmware does not support RGsB at all. It will only ever output YPbPr. There is a jumper option to output a very different digital signal for use with the RGBtoHDMI upscaler, but this is no use for a direct connection to an RGB monitor.

The A-Video board hardware itself is basically identical to the C64 component video mod board. It only has different output connectors (RCA instead of TRRS) and lacks the analog circuit needed for the C64. So you can easily use a C64 mod for the Atari when flashing the Atari firmware.

If you really, really, really want an RGB option, I could modify the firmware.

Icelvlan88 commented 4 years ago

I was considering trying to use this if it work for an Atari 5200. The reason I prefer RGB is the way it looks through the framemeister and I typically use Genesis 2 RGB cables which use TTL.

c0pperdragon commented 4 years ago

So I guess, it is your intention to build a Genesis 2 - compatible A/V port into your atari 5200. This is a pretty cool idea to re-use the rest of your setup.

When your genesis cable has the usual 470 Ohm attenuation resistor for the csync line, it will happily accept any digital sync signal between 2V and 7V. Below the 2V the sync may no longer be reliably detectable and above 7V it may become dangerous to the receiver. With a 3.3V digital sync signal you are absolutely fine here.

A second matter are probably the 75 Ohm attenuation resistors that also seem to be built into the cable on the R, G, B lines. I am not sure about this, but the schematics for the cable I quickly found all have these. So to avoid the picture to be to dark you would need to bridge the 75 Ohm resistors on the FPGA board to compensate for that. It seems that the genesis console ommited the usual 75 Ohm output driver resistors which where then built into the cable.

I am positive now that I will actually add an RGsB output mode to the firmware anyway for exactly this kind of use cases.