5 May
2010
5 May
'10
12:54 p.m.
Those were gimmicks, too, in their day - we used to
spend quite a bit
of effort to adapt Atari joysticks to PET User Ports (one is easy, two
joysticks takes a bit of effort because there are five switches and
eight primary bits - mostly folks used diodes, but I think there was
I am wondering how you did this...
IIRC, there are 5 swithces for the joystick, up, down, left, right, OK,
up and down can't be actuated simultaneously, nor can left and right. But
combinations such as up-and-right are possible, at least on any decent
joystick. And the fire button is independant of the joystick position.
That means there are 9 states for the joystick (centre, U, D, L, R, UL,
UR, DL, DR -- using the obvious abbreviations). That takes 4 bits to
encode. Exactly the same number as if you fed each switch into its own
port line.
So you would still need 10 port lines...
I I had to do it on an 8 bit user port, I think I would use a '157 mux to
select between the 2 joysticks (4 bits each, going to 4 bits on the
port). And an port line configured as an output to switch between them.
And finally 2 more port inputs (a totla of 7 of the 8 user prot lines
used) for the fire buttons.
-tony