Egan Ford

Is the blink rate adjustable? If not, it is normal for different
systems to have different blink rates? Thanks.

Steve Nickolas

On Sun, 8 Jan 2012, Egan Ford wrote:

> Is the blink rate adjustable? If not, it is normal for different
> systems to have different blink rates? Thanks.

I know of no way to adjust it. I don't even know what it is and have
usually eyeballed it.

-uso.

David Empson

Egan Ford <datajerk@gmail.com> wrote:

> Is the blink rate adjustable? If not, it is normal for different
> systems to have different blink rates? Thanks.

The blink rate of flashing text is not adjustable.

In the Apple IIe and later, it is controlled by a counter clocked off
the video scanner inside the IOU chip. It is a fixed rate which will be
identical for every machine. According to "Understanding the Apple IIe"
by Jim Sather, it is 1.87 Hz in the US IIe model. There is probably a
small difference with the International IIe, since its video circuits
are clocked at 14.25 MHz instead of 14.31818 MHz.

In the Apple ][ and ][+, the flash timing is controlled by a simple
analog delay circuit. I don't have a detailed schematic handy, but I
expect it is an R-C delay circuit (resistor and capacitor). There will
be a fair amount of variation between specific machines due to the
margin of error in the resistor and capacity rating (potentially in the
order of +/- 10% from optimum, depending on the rating of the components
Apple used, and it may vary even more as the capacitors age).

--
David Empson
dempson@actrix.gen.nz

Patrick Schaefer

Am 08.01.2012 09:26 schrieb Egan Ford:

> Is the blink rate adjustable? If not, it is normal for different
> systems to have different blink rates? Thanks.

Yes, but only in hardware. There is a 555 timer on the mainboard
(position B3) that generates the flash timing. Change the resistor
values to adjust frequency and duty cycle. Read the NE555 datasheet (at
www.alldatasheet.com) for further details.


Patrick

D Finnigan

Egan Ford <datajerk@gmail.com> wrote:
> Is the blink rate adjustable? If not, it is normal for different
> systems to have different blink rates? Thanks.

Yes, on the II and II Plus, let it heat up a bit (as the machine is on for
a while). Text will blink faster! This is from my personal experience.

Michael J. Mahon

D Finnigan <dog_cow@macgui.com> wrote:
> Egan Ford <datajerk@gmail.com> wrote:
>> Is the blink rate adjustable? If not, it is normal for different
>> systems to have different blink rates? Thanks.
>
> Yes, on the II and II Plus, let it heat up a bit (as the machine is on for
> a while). Text will blink faster! This is from my personal experience.

In that case, your timing capacitor is probably leaking (electrically).

Tolerances on capacitors are rarely better than +/-20%.

-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon