| Intellivision |
· For game design, Intellivision II was supposed to be identical to the original - the main chips and their functions are the same as described for the Intellivision Technical Overview. But there turned out to be a major difference - when Intellivision II was released, it was discovered that 3 of Coleco's Intellivision games on the market, Donkey Kong, Mouse Trap and Carnival, would not work on it. Why not? At first, Mattel said it wasn't sure - maybe software changes needed for the System Changer to work were causing the problems. But as more and more games in development at Mattel were found not to work with the Intellivision II, programmers were filled in on the truth - but only on a one-to-one, need-to-know basis. The reason the Intellivision II doesn't work with the Coleco games is because it was designed not to. The EXEC contains a subroutine to display the Mattel copyright notice, but since a competitor's game would not use this routine, that location could have anything in it. So when the Intellivision II EXEC checks on a particular bit in that location and finds it isn't “properly” set, the EXEC doesn't allow the game to play. With a valid date in that location, the bit will be set; anything else and there is only a 50-50 chance the bit will be set. This was a deliberate attempt to render competitors' cartridges useless, and therefore it may very well have been illegal. But as game size went from 4K to 8K and larger, more Mattel programmers started using special title screens that bypassed the EXEC copyright routine. These programmers had to be told to make sure the bit was set. Of course, once the Intellivision II was on the market, competitors were able to figure out how to make their new cartridges work on it. The programmer of the original EXEC, David Rolfe, is reasonably sure the EXEC II changes weren’t done by him, as he knew better than anyone that any substantial changes to the EXEC would very likely “break” a number of games already released.
· Coleco work-around mod: Hook up a momentary contact switch between pins #38 and #40 on the cartridge port (looking at the front of the system, count from the back of the unit, to the 3rd and 4th pins of the cartridge port - the row of pins that you can get to easily, not the lower ones). Turn the system on and press the switch. It may take repeated tries for the game to work.
· BUG: The change in the Intellivision II EXEC also introduced a slight timing error in the system. Minor problems with sound effects started cropping up. Bill Goodrich was the first to notice this while playing Space Spartans. Once aware of this, the programmers were able to get around it, but two already released games were affected - Space Spartans and Shark! Shark!. The biggest timing problem appeared years later, with INTV's release of Super Pro Football. The cartridges were manufactured before anyone tried the game in an Intellivision II -- and discovered that the quarterback didn't appear on the screen until after the ball was hiked. An errata slip had to be included with the (already-printed) instructions. {BSR}
