DanBoris' Tech Blog

Great stuff I'd always wondered how games worked w/out a CPU.

Great stuff I'd always wondered how games worked w/out a CPU.

 

Thanks! I was also quite curious about how they worked which is what led me to start writing this blog!

It's amazing how much stuff can be replaced by microprocessors. A 6507 and RRIOT chip (RAM, ROM, I/O, and timer) could probably replace most of the circuitry in Pong even without using any custom logic.

 

If I were trying do design a 6507-based PONG, I'd probably have a hardware counter chain to generate horizontal sync, a slip-counter to generate the ball (horizontal only), a latch to enable/disable the ball, a '165 to generate the paddles, net, and scores (along with a few gates to activate it). And a 556 to read the paddles I guess, along with a '741 to handle input.

 

Still, it's impressive what people were able to design using just discrete circuitry. I think Pong is interesting because it took a very different design approach from Ralph Baer's machines--one which served well for a few years before microprocessors took over.

It's even more impressive to look at some of the later discreet logic games. I recently refurbished a Sega Monaco GP machine which was one of the last discreet logic games. It's amazing to think that game doesn't have a microprocessor. Actually in the case of that game I have wondered why they chose to go without a processor. It was released in 1980 and I can't image that it would have saved them any money going pure logic instead of a processor.

 

Dan

Wow - I would never had expected that to be discrete.

 

The circuit boards look pretty complex, I suspect it would have taken a while to design. Perhaps when they started the CPUs where still too expensive, but when the CPUs became less expense they were far enough along that it didn't make sense to scrap it.

The circuit boards look pretty complex, I suspect it would have taken a while to design. Perhaps when they started the CPUs where still too expensive, but when the CPUs became less expense they were far enough along that it didn't make sense to scrap it.

 

Perhaps. I could certainly understand doing the game logic as discrete. But the scoring/ranking circuitry? That alone used over fifty chips, and could have been done very easily with a microprocessor.

 

Probably a 650x, a couple RAMs (1Kx4 should be fine), a ROM, a few of 373's (one for every ten display digits), a 10-output Johnson counter, a few driving transistors, a 555 and a few discretes, and probably about five more 74xx chips.

 

Really a very straightforward design. Alternatively, one could use a non-multiplexed display with one 373 per digit.

Wow, look at all those chips on the Monaco boards! Dan are you going to tackle Monaco GP next?