Re: Hacking the Laser 128EX/2

[Rubywand <rubywand@swbell.net>]

Supertimer writes ...
> 
 ....

> Alas, I checked more closely and the 3.6Mhz crystal is not color burst.
> XTAL3 is printed with "3.6864 SUNNY" so it is truly a 3.6Mhz crystal.
> XTAL1, however, is printer with "14.31818 SUNNY" so this crystal provides
> the Apple II signal you speak of.
> 
> The main problem I have is that these are not the same types of oscillators
> as on the TransWarp GS or Zip GS.  They only have two legs!  The TWGS
> ones have four legs.  Any ideas?
>

     They are just the crystal part of the osc circuit. (Osc modules have the
crystal plus the rest of the circuitry in a nice compact package.)
 
 ....
> 
> The video system appears completely isolated.  Unlike the Apple II, the
> Laser's motherboard runs at 3.6Mhz (thus, all the RAM chips are 120ns).
> However, I noticed that there are 64k of 150ns chips (two chips=64k). From
> the Laser advertisements, this is the "video RAM."  Apparently, they've
> solved the timing problems of a faster motherboard by having separate
> memory for video.  Neat!  Now this is not as efficient, obviously. There is
> 192k of memory on the main motherboard, but only 128k shows up as
> system RAM.

     The "Video RAM" sounds like some kind of shadowing arrangement. It seems
like the Laser 128EX/2 should be able to offer additional video modes.


     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.



Rubywand