20 Oct
2018
20 Oct
'18
11:05 a.m.
On Sat, Oct 20, 2018 at 6:52 PM Fred Cisin via cctalk
<cctalk at classiccmp.org> wrote:
Similarly, although they sold a joystick board, they
didn't sell
joysticks. DA15 connector for two joysticks.
In some of the documentation, the sketch of a joystick was clearly the
Radio Shack Coco joystick (which needed a different connector)
And is electrically different.
The CoCo Joystick is a potential divider across the 5V rail. Moving the
joystick varies the output voltage (2 voltages per joystick, X and Y). This
is fed into a 6 bit ADC (actually a 6 bit DAC, a comparator and some
firmware).
The IBM PC Joystick (like the Apple ][ ones) is a pair of variable
resistors. This are the timing resistors in monostable circuits, acutally
an NE558 chip (Think of it as being 4 555 timers always connected as
monostables in one package). The software triggers the monostables
then sees how long they take to flip back again.
I assume the PCjr Joystick is like the PC one, electrically, but I don't
feel like going upstairs to check the TechRef.
-tony