Re: 14MHz 65816??

[dempson@actrix.gen.nz (David Empson)]

In article <4ut5gc$gk1@ganesh.lm.com>, mportune@telerama.lm.com (Matt
Portune) wrote:

>Tony Cianfaglione (tony@ccn.cs.dal.ca) wrote:
>>    I have been in contact with Western Digital regarding their 14 MHz 
>> 65816 chip which they tell me fits onto the accelerator cards such as the 
>> TransWarp GS or Zip GS.  They were not sure if it would replace the stock 
>> GS chip that plugs into the motherboard, which is what I want to do.  I 
>> find the various accelerator cards too buggy to rely on.

>> Is anyone familiar with the 14 MHz chips and can you get one to plug into
>> the motherboard and chuck the accelerator cards altogether?

>        Unfortunately, the answer is no.  The new 816's put out by WDC 
>(Western Design Center BTW) are not the long, rectangular chips that the 
>GS uses.

Even if WDC did make dual-in-line versions of the 14 MHz 65816, putting it
into the IIgs motherboard would not achieve anything.  The speed of the
computer is controlled by a clock signal provided to the CPU, which is
under the control of the FPI chip (Fast Processor Interface).  The
ultimate source is the 28.63636 MHz crystal oscillator under the power
supply.

You cannot change the oscillator frequency significantly without stopping
the whole computer from working - almost everything is dependent on the
precise frequency generated, including the video circuitry.

This is why an accelerator card is required if you want to make the
machine run faster - the card must access the main IIgs memory at the same
speed as the normal processor (by synchronizing with the clock signal from
the IIgs), but it can save a copy of the data in its own fast cache
memory, then run at full speed if it needs to access the same data again. 
It can also run at full speed for any CPU cycles that do not actually need
to access memory.

Putting a fast CPU in the motherboard would gain nothing - the rated speed
of the CPU is the MAXIMUM speed at which it will operate, but it will only
achieve that speed if the external clock signal is adjusted accordingly.

>>    They keep crashing in the middle of vital projects and I'm forced to 
>> disable the cards and run at the native speed.

This could be due to a fauly accelerator (my original ZIP GS started doing
this about a year after I bought it, but my second one has been fine).  It
might also be due to electronic noise within the computer, overheating or
power supply overload.

Is the machine that has problems a ROM 1 IIgs?  They are more likely to
have problems with an accelerator than a ROM 3 (the ROM 3 has a cleaner
motherboard design, and it uses less power).

What other cards are installed in the machine?  If you have several other
cards, or power-hungry cards like the PC Transporter, you are more likely
to have problems with accelerators.

-- 
David Empson
dempson@actrix.gen.nz
Snail Mail: P.O. Box 27-103, Wellington, New Zealand