[Coco] Coco3 joystick action survey

[Stan Blazejewski]

G'day Robert,

Keep in mind that the standard joystick leads are not shielded & were prone to
pick up 'noise' when run close to the monitor/TV.  I replaced my leads with
shielded lead when I had a similar problem, made it rock solid. Try running the
lead as far from the screen as possible & see if that makes 'any' difference.

On Mon, 10 Mar 2008 23:01:26 -0400, you wrote:

>I could use some help with this. I've been acting as a beta tester on a 
>game for the Coco3. The game has a cursor that is moved around on the 
>screen to select items. At the moment, there are two other testers and 
>the cursor action on my system seems to be unique in that the cursor 
>jitters. That is the pointer at most locations on the screen is never 
>stationary but always jiggles slightly. The cursor is completely steady 
>on the other systems.
>
>This has been very frustrating for the programmer because it is unlikely 
>that my system is unique and it has been impossible (using software) to 
>remove the jitter. What I would like to find out is how many Coco3s 
>exhibit jitter in the joystick values vs those that don't. I'm asking 
>readers to run the short Basic program below and very slowly move 
>joystick (right, left, or both) around the screen. Try to find a 
>locations where the value obtained by the JOYSTK(#) command is not 
>stable. Please report back here what you see.
>
>10 POKE &HFFD9,0       2MHz CPU clock
>20 WIDTH80         or you can use 40
>30 FOR I=0 TO 1 STEP 0
>40 EXEC &HA9DE         the ROM joystick routine
>50 PRINT PEEK(&H15A),PEEK(&H15B),PEEK(&H15C),PEEK(&H15D)
>60 NEXT
>
>The values at $15A and $15B are for the right stick and those at $15C 
>and $15D the left. On my system, the values are stable at 1MHz
>(POKE &HFFD8,0) but unstable at many positions at 2MHz. I've tried this 
>with two Coco3s serial numbers 1001703 and 1308368. I've used three 
>joysticks, two deluxe and one regular. There is jitter for all at 2MHz 
>with the ROM routine and worse jitter in the game under development.
>
>The ROM routine for reading the joystick is slower than that used in the 
>game which may be why it works at 1MHz. The main questions are whether 
>this is a quality control issue in the Coco3 design and what if anything 
>can be done about it.
>
>Both the game routine and the ROM routine are stuck with the resolution 
>of the internal DAC, 64 steps. A joystick being a continuously variable 
>resistor can easily be set at values in between those of any two DAC 
>steps. Depending on the circuit design intermediate values could cause 
>oscillation between the two adjacent steps. This could be caused by 
>inadequate ICs or by noise on the power supply. I've put a scope on my 
>Cocos and they meet or exceed the waveforms in the service manual.
>
>Hopefully there will lots of response to this request for help. I'd like 
>to solve this problem and the programmer wants to solve this more than I 
>do.  :)
--

Australia isn't "down under", it's "off to one side"!

www.cobracat.com (home of the Australian Cobra Catamaran)
www.parkdaleyc.com (where most of them sail)
http://groups.yahoo.com/group/cobra-cat/ (where we talk about them)