Lacescan Derryck Croker looks through the square window to lift the blinds on a hardware project that will broaden your horizons... A development of the original Public Domain overscan modification, LaceScan improves upon it in both hard and software. The simplicity of the circuit belies the added ease of use and comfort of working with a screen that displays less of the useless border and more usable pixels. The two integrated circuits, a resistor and an optional switch are readily available from electronics stores such as Maplin. The price to pay is that a little surgery has to be carried out on the ST's printed circuit board, so this may not be a project for the faint-hearted! Neither is the hardware suitable for installation in STe computers due to rationalisation of chip design. Fear not though, STe owners can still use the software-only large screen emulator, read on! The circuit can be built on stripboard or by piggy-backing the chips on top of others on the motherboard as suggested in the ST-Guide hypertext. My own preference is to use a printed circuit board, a suitable design is included on the reader disk ready for printing to drafting film and photoetching. Naturally neither the author of the LaceScan package, myself nor the Atari Computing Group can be held responsible for any damage caused by the fitting of this project, however if you know one end of a soldering iron from the other then read on! KICKING OVER THE TRACES This is the scary bit folks. We have to follow the Display Enable signal that is generated by the Glue chip and interrupt it by cutting through some tracks in order to introduce our little gadget. Soldering thin wires to the vias (where tracks pass from one side of the printed circuit board to the other) poses less risk of the fine tracks lifting. A sharp craft knife wielded with due care will soon take care of the necessary surgery. DRIVING A HARD BARGAIN With the LaceScan driver, the optional large screen emulator and mouse accelerator copied into the Auto folder and the computer rebooting, a press of the left [Shift] key leads to the initial setup screen. Usage of the keys described thereon will adjust the display to the largest that your particular monitor (mono or colour) will take without distortion of the screen edges. Final adjustment of the picture positioning controls on the monitor may be required to obtain the very best results. Some of the slots available from this screen allow the recentralisation of the screen image for non-overscanned screens, a rather nifty idea! MOVING ON TO BIGGER THINGS The optional large screen emulation feature of LaceScan can be enjoyed by STe owners as well, and offers such goodies as TT high (that's a whopping 1024*960 pixels). The trade-off is that such emulation can never be as fast as the real thing, but it is quite usable none-the-less. Accessing these emulated screens can be carried out by a variety of means, there are various configurable inf files that can be copied and renamed as required at boot time with a boot manager such as XBoot, or copied from the desktop. Mono users may like to use the GEN_MONO.INF renamed as LACE_EMU.INF, this file is missing the colour monitor specific commands and is therefore a little less complex. A rather clever piece of trickery with the 'Set resolution' buttons under the 'Options...' menu allows the reinitialisation which is required to register the new resolution by clicking on 'Medium'. Naturally this isn't possible with replacement desktops where this option isn't available, such as Teradesk. Quit back to the Atari desktop or reboot with the required emulation set. MagiC/MagxDesk owners can use the 'Change Resolution...' menu item found in later versions to perform the same task, and once an emulation is active SET_LACE.ACC can be used to further tweak the results or load another emulation as required. THE BOTTOM LINE Most software is properly written to GEM guidelines and so are perfectly happy running at screen sizes other than the assumed ones, but some older (and some not so well programmed) ones can and do give trouble. I was disappointed to find that I was not able to run Calamus 1.09N in either overscan or under emulation modes, a garbled icon toolbox does not make for easy navigation through this quite complex program. LaceScan attempts to overcome this problem with a hot-key command to switch the overscan mode off, however my ST has trouble with this and does not synchronise properly until a program runs and initialises (with the obvious problem of the difficulty of actually finding one to run from the Desktop!). There is no reason to expect this is more than the usual variations in tolerances from machine to machine however, and the tools folder in the distribution contains a small program LACE_LOK.PRG that can be assigned to a function key that (on my ST) quickly regains stability. Otherwise LaceScan is quite happy with the usual system enhancements such as MagiC and NVDI. LACESCAN LACESCAN35.ZIP is shareware from Ulf Ronald Andersson. Ronald suggests that you send whatever you think the package is worth, from the UK a banknote in pounds sterling is fine. It is available from BBSs connected to the FanFiles network, or by ftp from http://www.oden.se/~dlanor/ from where the latest version is always available. THE COMPETITION Overscan (PD): A much simplified circuit, no emulation of other screen modes. Should be available from most BBSs and ftp sites. AutoSwitch OverScan (commercial): The complexity of the circuit and additional installation steps means that the switching on and off of the overscan mode is problem free, an INF file details programs that aren't overscan-friendly and will switch overscan on and off automatically as required. However compatibility between this feature and MagiC may still be an issue. OverScan GMBH http://www.overscan.com/ Price: 90DM (BOXOUT) Overscan? The difference between the standard screen sizes for the three resolutions that the ST can produce (low, medium and high), and the maximum that could be displayed on a particular monitor results in the familiar black border. Some users have adjusted the controls to zoom the display out to the edges of the screen, this merely results in the same number of pixels but at a larger size. The Overscan concept fools the video shifter chip by lengthening the Display Enable signal into switching from displaying pallete 0 (that's the pallete for the familiar black border) earlier and later in the cycle to video memory, as a result the visible screen size is extended or overscanned. (PHOTO) Interior layouts vary between STs, take care to follow the hypertext carefully. Remember, measure twice and cut once. (PHOTO) The LaceScan module fits neatly on top of the Modulator using double-sided sticky foam tape. (SCREENGRAB) BEFORE.GIF This will be the last time that most programs will peer out at you at 640*400 (SCREENGRAB) OVERSCAN.GIF A wider window on the world, this is overscanned 672*476. This size is limited by the constraints of my monitor, your mileage may vary as they say! (SCREENGRAB) 1024*960.GIF This scrolling overscanned window on a virtual 1024*960 screen is as close as many will get to a real TT.