Asteroids Chip Question

D_Harris

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Is anyone familiar with the 74161 counter chip at location C5? It is said to deal with the Non maskable interrupt pin on the cpu, and I'm wondering what it's function is, and whether it can be manipulated to effect game speed.(Scoring rate).

Also did all Asteroids PCBs by default come with a 12.096 crystal?

Thanks.

Darren Harris
Staten Island, New York.
 
Good to see you *really* researched this question before posting... not like this topic hasn't been beaten to death on RGVAC in the past.

This is the standard speedup that replaces C5:
Asteroids_Speedup.jpg
 
That's all greek to me since I know nothing about schematics.

The questions were simple, and the RGVAC search engine is not working.(I get no hits when I put in "Z80").

Darren Harris
Staten Island, New York.
 
Good to see you *really* researched this question before posting... not like this topic hasn't been beaten to death on RGVAC in the past.

This is the standard speedup that replaces C5:

I remember seeing this in RGVAC back in 2002 or so, I never actually thought about doing the mod, but thanks for the schematic. Might be something fun to try at some point.

Luke
 
I remember seeing this in RGVAC back in 2002 or so, I never actually thought about doing the mod, but thanks for the schematic. Might be something fun to try at some point.

It was sold as an aftermarket add-on board... i'm sure someone's got a speedup kit that they took off their boards and didn't throw away. You can just vary the NMI period at 1/3khz increments by playing with the A-D inputs on C5, but that doesn't give you much granularity.

I've seen another kit with dips on it (also with its own 555 on-board to generate timing), that makes the speed up easily configurable.
 
Well no...
I know certain individuals are using crystals other than the one mentioned. So I wondered whether Atari was consistent in this respect.

Do you really think Atari stocked a bunch of different speeds of crystals, and just put whatever was handy on boards?

Pretty easy to look at a board and see if the crystal's been swapped...
 
Do you really think Atari stocked a bunch of different speeds of crystals, and just put whatever was handy on boards?

Pretty easy to look at a board and see if the crystal's been swapped...

I have no idea what Atari did.

And looking at a PCB will not answer my question.

Darren Harris
Staten Island, New York.
 
It's nice to see two old friends getting along.....



;
 
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