RE: Star Wars/Wells Gardner 6100 Problem

Yeah, that's basically what I was suggesting before. You have a little
state-machine in the PAL that counts for a while while holding Reset low
and then releases it until the switch changes state again.

A 555 or 74LS123 would probably do the job as well, although I have a
religious aversion to anything that uses resistors or caps for timing
elements in stuff I make. I'm sure they're perfectly OK, they just make
me nervous. ;-)

Actually, now that I think about it, you might be able to do it with
just a double-pole, double throw (break before make) switch and an
open-collector driver (like a 74LS06? '07? Don't remember...). Tie the
output of one of the OC drivers to RESET on the 6809 with a pull-up (or
pull-down depending on if the OC driver is inverting or not). On half
the switch, tie common to the input of the driver, and tie either pole
to GND (or +5V depending on inversion or not). Use the other half of
the switch with common going to the select line on the ESB daughtercard,
and one pole going to +5, the other to GND:

               /|
              / | 47Kohm
  /RESET----o<oc|-----+------/\/\/\/\------+5Vdc
              \ | |
               \| |
                      |
            GND---O O O---GND
                DP/DT SWITCH
            +5V---O O O---GND
                      |
                      |
            To SW/ESB Daughtercard
 
So, if I'm thinking of this right-- When a game is selected, /RESET on
the 6809 is high (normal operation). When you switch games, the center
pole will "open" from GND for a couple hundred milliseconds and the
driver will yank /RESET low (reseting the game), then when the switch
makes contact (and bounces for a while) GND will be back and /RESET will
go high again.

Probably not the "cleanest" reset on the planet, but it'd probably
work... You might even get away with leaving out the OC driver and just
use a series resistor to /RESET with either end of the switch at +5V and
a pulldown to GND "in the middle". (although the watchdog would have to
"fight" the +5V sourced when a game is selected... still probably work
though.)

-Clay

> ----------
> From: John Robertson[SMTP:jrr@flippers.com]
> Reply To: vectorlist@mcfeeley.cc.utexas.edu
> Sent: Wednesday, February 03, 1999 8:10 AM
> To: vectorlist@mcfeeley.cc.utexas.edu
> Subject: Re: Star Wars/Wells Gardner 6100 Problem
>
> What if the game change switch had a small circuit added that forced a
> reset that lasted X amount of time? A 555 timer could be kludged in
> pretty easily...or it could just pull the MPU reset down...
>
> John :-#)#
>
Received on Wed Feb 3 11:03:17 1999