Re: Hacking the Laser 128EX/2

[supertimer@aol.com (Supertimer)]

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.

Shucks, I was afraid you'd say that.

Still, I might try to change the crystal just to see what happens.  What's the
worst that could happen?  I don't use the serial ports anyway.  ;-)

XTAL3 is pretty close in location to the CPU, but I guess that does not really
say much.  What I'm curious about is the labels.  If there is an XTAL1 and
an XTAL3, there should be an XTAL2.  I'll have to look more closely.  It may
be that XTAL2 would illuminate things.

Another thing is that even in "1Mhz mode" the Laser is not exactly 1Mhz
vis-a-vis the Apple IIe.  It is slightly different.  This might be what is
throwing
off the ZipChip as the ZipChip does not work on the EX/2.  It totally bombs
while booting up in 3.6Mhz mode.  In 1Mhz mode it works for a little bit,
then bombs.  I figure if the CPU clock is derived from XTAL1 (14Mhz), then
the timing should be exactly like an Apple IIe (in 1Mhz mode), but it is not.

The ZipChip works in the plain Laser 128, though.  Perhaps if a Laser 128
user would take a look at their motherboard and see if XTAL3 is present,
the mystery would be solved.  Meanwhile, I'll have to hunt for XTAL2.