Combat & Air-Sea Battle question

[RobR]

Sorry if this question has been asked and answered somewhere else, but I have never see it asked:

 

Why does Comabt and Air-Sea Battle have a time limit of 2 min 15 sec? At first, I thought of the 7 bit Maximum number of 128, but that would equal 2 min 8 sec.

[Keatah]

This has been answered in detail before - from a programmer's perspective IIRC. Anyone remember the thread?

[SoundGammon]

Other games Star Ship, Street Racer, Indy 500 all had the time limit. Back before the 2600 came out, there were a lot of b&w game consoles that mainly played Pong variants. When these units were played for a long time or left on, they would "burn" the image into the screen! You could then watch tv with an image of a pong or other design there all the time! This made a lot of consumers upset, so the early 2600 games would "time-out" and start to do the color shift to keep burn-in from happening to a limit. Even variations of the game used different color schemes to help keep burn-it low. I remember a woman who loved Tetris on the NES and would play it for hours, and later there was a permanent "tower" in the middle of their big projection screen!

[Keatah]

Early projector sets used super-bright CRT tubes. Very susceptible to burn in. But I don't believe the burn-in time out has anything to do with the 2:15 game limit.

[Rybags]

Actual frame-rate of the 2600 is usually less than broadcast (59.97 for NTSC) - 59.9227 should be the rate for a 262 scanline display.

 

But still the maths doesn't help there - it adds barely 1/10th of a second.

 

A look at the program code would probably reveal what's going on. Maybe tied to the RIOT timers ?

[karokoenig]

Or they just recycled that piece of code several times.

[Rybags]

I think I've worked it out.

 

Time counter starts with value $80 and gets incremented once every 64th frame = 8192 frames total game time.

 

8192 / 60 = 136.53 seconds

8192 / 59.97 = 136.6 seconds

8192 / 59.9227 = 136.7 seconds

 

High bit of counter likely used as "game in progress" flag. Simple compare can be used as trigger to flash score during final part of game.

Edited April 25, 2014 by Rybags

[RobR]

Other games Star Ship, Street Racer, Indy 500 all had the time limit. Back before the 2600 came out, there were a lot of b&w game consoles that mainly played Pong variants. When these units were played for a long time or left on, they would "burn" the image into the screen! You could then watch tv with an image of a pong or other design there all the time! This made a lot of consumers upset, so the early 2600 games would "time-out" and start to do the color shift to keep burn-in from happening to a limit. Even variations of the game used different color schemes to help keep burn-it low. I remember a woman who loved Tetris on the NES and would play it for hours, and later there was a permanent "tower" in the middle of their big projection screen!

I know about the "burn in" effect, but I was talking about the in game timer. Just seemed a weird #, that's all

[Rybags]

Sort of weird. Maybe they wanted 2 minute game time and the "every 64th" turned out the best compromise.

There's a counter that's incremented every frame, no doubt it probably gets used for other things as well.

Checking for "every 64th" is easy, just AND #$3F and Z flag set = 64th frame.

 

They could easily enough had made it 2 minutes almost exactly by setting the initial value differently at game start - a value of $90 instead of $80 would probably be sufficient.

[Wickeycolumbus]

This has been answered in detail before - from a programmer's perspective IIRC. Anyone remember the thread?

Here's a relevant post by Joe Decuir (in a similar topic):

 

http://atariage.com/forums/topic/43549-always-wondered-and-youll-know-the-answer/?p=1683294