dlm (11/30/82)
The last thing I heard about the ATARI CX70 light pen is that ATARI abandoned its development since they could not get it to work correctly. The hardware still supports a light pen ( ANTIC? ) and I have seen independent manufactures offer light pens. The atari handles light pens by reading the horizontal and vertical position registers whenever the pin for the trigger button is activated. It is possible to demonstrate this by simply entering a basic program to continuously read these locations ( RAM low memory ) and press the joystick button everyonce in a while. This function is done entirely in hardware, and the light pen position registers in hardware are copied to RAM during vertical blank, as are the other hardware registers.