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Using the STB Graphics Plus II board and a question about RAM [message #80933] Tue, 04 June 2013 00:01
Originally posted by: johnhi@tekig.UUCP (John Higley)
Message-ID: <2373@tekig.UUCP>
Date: Mon, 5-Nov-84 12:16:46 EST
Article-I.D.: tekig.2373
Posted: Mon Nov  5 12:16:46 1984
Date-Received: Thu, 8-Nov-84 00:19:27 EST
Organization: Tektronix, Beaverton OR
Lines: 45


  A friend of mine has in his system an STB Graphics Plus II board which
combines the monochrome and color video circuits as well as a printer
interface and the ability to run high resolution monochrome graphics on one
board.  He is using this board with and Amdek 310A monitor which is IBM
compatible for both the monochrome and color modes (it is a digital
monochrome monitor).

  As anyone out there using an Amdek monitor with one of the multipurpose
graphics boards may have noticed, the Amdek monitor does not center both the
monochrome and the 'color' pictures.  One method commonly used by some people
is the mode command's lt parameter which allows the shifting of the color
picture to the left to bring it into center.  This may be unsatisfactory to
some users.

  We have come up with a simple mod to the Amdek monitor which causes it to
automatically sync up to either of the two frequencies required and produce
an image which is in the center of the screen for either mono or color modes
with no user intervention (no need to use the lt parameter or adjust the
horizontal pot on the monitor).  This method involves adding another one-shot
to the monitor.  If any one is interested in the schematic for this I will
try to create a readable version of it for electronic mailing.  For those who
would like a less than perfect centering there is a one resistor mod:

  Attach a 100K resistor between the anode of a diode (SR405) on the flyback
  transformer (pin 3) and pin 7 of the timing circuit (IC 701).

This synchronizes the timing to the end of sweep pulse of the monitor.  It
does however leave some offset and may not satisfy the perfectionist.

  Care should be taken in applying either of these mods as I cannot guarantee
your work and you should try to gain an understanding of the changes before
you make them.

  Now for the question:  Has anyone converted their 256K max mother board to
use the 256K DRAMs and therefore contain the maximum 640K of RAM?  If so
please pass that information on to me (or the net).

					John Higley

Disclaimer:  The above article should in no way be construed as the opinions
of my company.  No guarantee exists either expressed or implied.
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