Re: Hacking the Laser 128EX/2

[supertimer@aol.com (Supertimer)]

Rubywand <rubywand@swbell.net> wrote:

>Supertimer writes ...
>> 
>> Ok, so the Laser 128EX/2 (and the 128EX) operates at 3.6Mhz.
>> But why stop there?  There has got to be a way to boost the
>> speed above 3.6Mhz.  Now before anyone says ZipChip, it does
>> not work with the EX/2 (or, I suspect, the EX).
>> 
>> However, I looked around the motherboard and found two
>> crystals.  At location XTAL1 is a 14Mhz crystal.  At location
>> XTAL3 is a 3.6Mhz crystal.  Does anyone know if the crystal
>> at location XTAL3 controls the CPU?  I'd like to boost the
>> speed of the 128EX/2.
>> 
>> By the way, all the RAM chips are socketted, so I could put
>> in faster ones too.  Currently, they are 120ns chips (faster
>> than the ones in the IIe, for example).
>
>     The "14MHz" may be 14.318MHz, as in the Apple II. It can be divided down
>to get the color burst signal (3.5795MHz) and assorted Apple II frequencies.
>
>     So, if the Laser really runs at 3.6MHz, the 3.6MHz crystal is likely to
be
>the one setting the uP clock frequency. What's kind of odd is that Laser
>wouldn't just use the color burst frequency-- 3.5795MHz is not a whole lot
>slower than 3.6MHz.
>
>     Which leads to an alternative explanation for the two crystals. That is,
>"3.6MHz" is really 3.5795MHz and this is the uP clock _and_ color burst. The
>"14MHz" osc could be used to supply Apple II compatible signals. Using two
>oscillators could eliminate some countdown chain IC's and reduce cost.

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?

>     If the "3.6MHz" osc supplies both color burst and the uP clock, changing
>it to, say, 4MHz could mess up your color. A possible way around this would be
>to locate the line going to the up (and any other non-video stuff), cut it,
and
>use a new osc.

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.