Changes
Bryce
:You got me confused, I just woke up and had my first coffee, and then this! No, the buffer isn't a latch - it doesn't memorize anything. And the Com pin has no effect at all on the timings.
:The Com pin could theoretically indicate when the software reads the port, but that'd require that software deselects the joystick line after each read, which you can't trust on.
:More commonly Com changes at 1/50s rate (when reading the keyboard; which is read only each 6th interrupt). If the software reads only the joystick port, without keyboard, then Com would stay LOW forever.
:Oh, just noticed a bug in your circuit :-) the Com pin is an open collector output, so there should be a pull-up in your schematic... unless the 74LS240 is having internal pull-ups on the /OE pins(?)
