Re: Hacking the Laser 128EX/2

[cranem@athenet.net (Michael Crane)]

One of the first computers I owned was a Laser 128EX (not the EX/2).
It sounds like it was much the same as the EX/2 (I think the EX/2 had
a built in 3.5" drive instead of a 5.25" drive...not sure what else
might have been different.)  I do recall that it was capable of
running at 3.6Mhz and 1Mhz, but I am fairly certain it was also able
to run at 2.xMhz (don't remember the exact number.)  What I found more
interesting (and frustrating) was something in the architechture of
the machine prevented it from working (at all) with a 65802 chip
instead of the 65c02 it was shipped with.  I tried two different 802
chips in case one was bad, but they didn't work.  The same chips
worked just fine in "real" Apple //e systems.

On Thu, 15 Jul 1999 01:39:19 -0500, Rubywand <rubywand@swbell.net>
wrote:

>Rubywand wrote:
>>
> ....
>
>>>
>     Getting back to the oscillators, 3.6864MHz is an interesting frequency.
>It seems to be interger divisable to obtain all of the major telecom baud
>rates.
>
>     This could explain the choice of "3.6MHz" (instead of 4MHz) as the uP
>clock frequency. My guess is that the 3.6864MHz osc serves as both the uP
>clock and the base for generating serial port baud rates.
><<
>
>
>     Here's another possibility which, really, fits things better. Maybe the
>3.6864MHz osc is entirely devoted to baud rate generation. The "3.6MHz" number
>for the Laser's speed comes from 3.5795MHz. This, of course, is the color burst
>frequency which comes from dividing down 14.318MHz.
>
>     Since Laser needs to be Apple II compatible and it needs color burst,
>using color burst for the uP clock cuts costs and also links/syncs the uP clock
>to other important A2 frequencies. (And, if Laser ran at 3.6864MHz, it seems
>like marketing would advertise speed at "3.7MHz" rather than "3.6MHz".)
>
>     If the above is correct, you may be able to go to "7MHz" (7.16MHz) by
>using the 7M signal for your system clock. Otherwise, it looks like messing
>with the 3.6864MHz crystal will not help and you are pretty well locked into
>your current speed.
>
>
>
>Rubywand