NetNews Usenet Archive 1992 #20/NN_1992_20.iso/spool/comp/sys/acorn/tech/147

Internet Message Format | 1992-09-15 | 3.4 KB

Path: sparky!uunet!sun-barr!olivea!spool.mu.edu!yale.edu!ira.uka.de!rz.uni-karlsruhe.de!stepsun.uni-kl.de!tangram.informatik.uni-kl.de!m_sattle
From: [e-mail] (Matthias Sattler)
Newsgroups: comp.sys.acorn.tech
Subject: Re: Hi res modes
Message-ID: <[e-mail]>
Date: 15 Sep 92 17:19:24 GMT
References: <[e-mail]> <[e-mail]> <[e-mail]>
Sender: [e-mail]
Reply-To: [e-mail] (Matthias Sattler)
Distribution: comp
Organization: University of Kaiserslautern (Germany)
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In article <[e-mail]> [e-mail]
(Nick Smith) writes:

>In article <[e-mail]> [e-mail] (Ashley Stevens) writes:
>>In article <[e-mail]>
[e-mail] (Matthias Sattler) writes:
>>>
>>>I just replaced the 36 MHz quarz on the board of my A5000 by a 60 MHz
one. This
>>>had several results on my A5000.
>>>5.) The computer gets remarkably faster... >22000 Dhrystones in mode 21, 28
>>>    (with CPU 30 MHz) and I don't know why as well.
>>
>>The 36MHz clock also clocks the memory system. It's divided by 3 inside MEMC
>>(effectively). So using a 60MHz clock means you are now running your memory
>>system at 20MHz. Obviously this has a beneficial effect on your machine
>>speed...if it continues to work.
>>
>>Ashley Stevens, Design Engineer, Acorn Computer       [e-mail]
>
>That really is incredible ! Can Matthias please post details of his machine
>(RAM, which 2MB upgrade board, etc) ? And how reliably it works, etc.


Ok. I now prefer using 50 MHz VIDC clock meaning 16.6667 MHz RAM clock because
my vidc can do 50MHz pixel clock and the machine is only a few percent
slower...
(still >22000 Dhrystones in mode 21, 28).
I havn't modified anything but the quarz for the CPU and for the VIDC (+memory)
and I have no 2MB upgrade board yet(but soon). But I think every board will do
as the slow 70 ns RAMs fitted on the board are fast enough for the 20 MHz RAM
clock.
My A5000 runs perfectly stable with the modification for 6 month now. (with no
heat problems)

But there are a few effects I can't explain:

   - Very low res modes like mode 0 don't work any more,
     but this isn't so important.
   - 800X600 256 colours should work with 50 MHz pixel clock because the
     RAM clock is increased by the same factor but in fact it doesn't.
     (I think this is a bit disappointing to me)

   - And there is another phenomenon: the VIDC can be clocked higher if
     I cool it with cooling spray but the ARM 3 can't????!!!! WHY???????




PS:   The VIDC clock isn't necessarily connected to the system clock.
      For that reason old machines with a VIDC-enhancer don't get faster.
      (no faster RAM clock)

PPS:  Hello ARMLTD and VLSI. I have seen VLSI 386-Chipsets in 0.8 um technology
      BUT THE ARM IS STILL 2 um!!!!!!!! WHY!!!!!!! With that technology a 50MHz
      ARM 3 would be no problem......



Matthias Sattler

If you know my funny previously posted e-mail adress mail me, it is
still working.
But our local mail administrator told me that I should not publish it
any more...
*sniff*
(If someone posts my e-mail adress to this newsgroup then it isn't me
and I can't
do anythig about it..... *grin*)


snail mail:
Matthias Sattler
Hauptstrasse 41
6751 Heltersberg

GERMANY

Tel.: [phone]
      06333/63175