             AN IMPLEMENTATION OF THE LACESCAN CIRTUIT

This text contains some details on implementation of a LaceScan circuit for
increasing the screen resolution on a MegaST computer.

NOTE: LaceScan circuit design is copyrighted  (c)1996 Ulf Ronald Andersson,
all rights reserved. This text  only contains a description of  a physical
implementation of Lacescan. Refer to LaceScan 3.5 documentation for details
on LaceScan itself.

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		                DISCLAIMER
 Although  this  modification  worked fine for me, it may not do so for you.
 I shall  NOT be  responsible for  any  damage, resulting  from  trying this
 modification,  to your computer and other equipment, or any  damage to any-
 body's life and health,  or any  galactic  imbalance  whatsoever.  Whatever
 you do, you do at your own risk.  Be advised that in an open computer there
 are  exposed  parts that are  at mains line voltage (i.e. 220V AC) and  you
 can easily get KILLED if you are not careful!
 ---------------------------------------------------------------------------

Picture LS.IMG contains details of the little board which I made  to install
LaceScan. I have found it convenient to make board with pins and to solder a
28-pin socket to the motherboard, between the PSU and the Megabus port. Just
several pins on the socket make contact with  the motherboard  (as marked in
the picture), on my motherboard  there is convenient  ground plane  at those
points. Other pins on the socket are shortened  so as not to touch anything,
but wires are soldered to some of them, leading to appropriate  positions to
obtain DE, HS, VS, etc. INCLUDING +5V. I used a ribbon (i.e flat)  cable for
these  as it could be layed  very tidily on  the  motherboard and  be routed
between the chips. Approximate routing is  showed with thin lines in P2.IMG.
Therefore, LaceScan hardware is just plugged into the socket,  together with
the wires leading from it to a switch which I found convenient to  locate on
the back  side of  the computer  (on a small plate attached  to  the shield,
where there is an opening for expansions on Mega's box). 

Original state of the video circuit can anytime  be restored by plugging-out
the LaceScan board and by installing a jumper wire in the socket, from DE-IN
to DE-OUT. 
 
Unfortunately, I could not squeeze a standard 28-pin socket  where  I wanted
LaceScan to be- there was no room. I sliced it in two, removed  a bit in the
middle and glued it back together with  Cyanoacrilate- so  now it is one pin
distance narrower than a standard 28-pin DIL socket.  You can  see that from
the sketch of the PCB. 

Picture P1.IMG shows convenient  locations to tap  the needed signals from a
MegaST motherboard. It is adapted from pictures contained  in  the  original
Overscan documentation (ref.2).  Hopefully the authors would not  mind  this
use of one part of their picture although it might be considered  stretching
the copyright a little bit.

References:

1: Ulf Ronald Andersson: Lacescan V3.5
2: Stefan Hartmann & Carsten Isakovic: Overscan documentation


                                                    Djordje Vukovic

                                                    e-mail:vdjole@EUnet.yu
