Re: IIc Mouse not moving vertically

[dempson@actrix.gen.nz (David Empson)]

Myles Fudge <Myles.Fudge@logicbbs.org> wrote:

> Lately my IIc mouse have not being moving vertically... only horizontally.
> The mouse pointer moves across the top of the screen okay, but it is stuck
> on that line.  I have been testing my mouse with ProTERM v3.0.  And this
> is the mouse I have had for years.  I notice that the mouse pointer
> character flickers if I move the mouse vertically, but the pointer stays
> on the top line of the screen.

The flicker is probably due to the software detecting a very small
horizontal movement while you are trying to move the mouse vertically.

>  I have tried two different mice and I assume now that the problem is with
> the IIc and not the mice.  Does anyone know of a common problem that
> prevents a IIc mouse from not moving vertically?

I'm not aware of any common problem that might cause this, but it is
certainly possible that there could be a motherboard fault that is
preventing the vertical movement signals from being detected.

Two of the pins on the connector provide a pulse train to the IIc as the
mouse moves vertically (pins 8 and 9).  One pulse is generated for each
unit of movement, and the phase relationship between the signals
determines the direction.

The IIc gets interrupted for each unit of movement (lots of overhead!),
and the main CPU is responsible for updating the mouse position data
accordingly.  The critical one is pin 9 (YMOVE): each rising edge on
this signal causes a vertical movement interrupt.

A fault could be due to a corroded pin or track.  If you want to
investigate further, can take apart your IIc and have a continuity
tester, check that the signal from pin 9 of the mouse/joystick port is
connected to pin 10 of the 40-pin IOU chip.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand