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When the T/S 1500 was released, Timex also released the T/S 1510 cartridge system. The T/S 1510 was a cartridge dock that plugged into a 1500 or 1000. Game cartridges were then plugged into the dock and when the 1500 was powered up, the game on the cartridge started up. For the 1000, a USR call was needed to start the game. The 1500 ROM was modified to check to see if the T/S 1510 and cartridge were plugged in on start up.