Re: IIGS Drive Questions

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

Juspion2002 <juspion2002@aol.com> wrote:

> I just got a IIGS yesterday and have run the different system disks it came
> with.  My question is why once the disk loads the GS/OS and is on the desktop,
> I hear a light ticking sound coming from the CPU.  I have two 3.5 drives and
> two 5.25 drives hooked up and I notice every time the system ticks, the 5.25
> drive lights blink.

This is caused by the Finder polling the 3.5" drives to see whether you
have ejected or inserted a disk.  The polling consists of selecting the
drive and reading a flag bit (it doesn't need to activate the drive
motor).

The select line is shared by the 5.25" and 3.5" drives, and there is an
"enable 3.5" output which causes the 3.5" drive to cut off the
daisy-chained enable signal to the 5.25" drives, but it cannot do this
fast enough to avoid a brief pulse on the LED of the 5.25" drive.

The sound you are hearing is due to electrical noise on the +12V rail
(or possibly the +5V rail) leaking into the sound circuitry.  The ROM
00/01 IIgs is most affected by this: the ROM 3 has improved sound
circuitry which is much less susceptible to noise.

-- 
David Empson
dempson@actrix.gen.nz