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SoundGammon

7800 R.I.O.T.

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We all know that the 2600/7800 use the riot chip, 6532, for controllers, ram and such, my question is I know there are 2 versions of the riot chip, 1 at 1mhz and 1 at 2mhz. I was wondering if the faster version would be better/faster in the 7800?

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Sometime way back I asked why it wasn't designed with the 2MHz version in the first place.

I'm not sure it ever got a solid answer but one theory was that maybe the 2MHz version would be unstable at 1.2MHz (for 2600 games). Apparently some old NMOS chips don't like running slow.

 

But it might also just be because they already had 1MHz chips and didn't want to spend money on new ones. Seems strange to do something that cheesy when designing a new console, but it wouldn't entirely surprise me. If that's the reason then maybe the 2MHz would work fine.

 

It wouldn't accomplish anything as a retrofit though. The Maria slows down the clock rate when the RIOT addresses are in use, so plugging in a 2MHz RIOT won't actually make it go any faster.

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I'm more interested in figuring out why they never bothered to connect the RIOT's interrupt line to the IRQ line of the Sally in the 7800 (although this was probably due to timing issues).

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I'm more interested in figuring out why they never bothered to connect the RIOT's interrupt line to the IRQ line of the Sally in the 7800 (although this was probably due to timing issues).

 

Yeah, that's a good question too. Very frustrating not to have that feature.

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Just found this thread while searching for details about RIOT.

 

I'm more interested in figuring out why they never bothered to connect the RIOT's interrupt line to the IRQ line of the Sally in the 7800 (although this was probably due to timing issues).

Is this confirmed?

That means the RIOT can't trigger an IRQ on the 7800?

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Just found this thread while searching for details about RIOT.

 

 

Is this confirmed?

That means the RIOT can't trigger an IRQ on the 7800?

 

Guessing it was because this could break some 2600 games if they did. Also, the maria is hooked up to /IRQ on the CPU for scanline interrupts as far as I know. Granted they could've wire OR'd the two sources and had some kind of disable on /IRQ to prevent any IRQs from occurring but didn't do it because it'd cost money. Atari was so cheap they didn't even include sound except from the TIA so I can see why they didn't include IRQ functionality from RIOT.

 

Timing would've been fine- /IRQ goes low until the CPU services it and manually clears it via the RIOT registers.

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