🚀 go-pugleaf

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.