LCD monitors and RISC OSBy Chris Williams. Published: 14th Mar 2004, 23:28:45 | Permalink | Printable
Shopping for TFT?Mini-guide Ages ago, a reader asked drobe.co.uk to write an article about LCD monitors and RISC OS, because he wanted to buy one and wondered how to choose one. The simple answer is: ask a dealer. This is basically because they're likely to be selling LCD monitors that they've tested with RISC OS and have appropriate Monitor Definition Files (MDFs) to drive the flat screen monitors. We've pestered a few dealers (see links at the end) for information and compiled a straight forward guide to LCD monitors with RISC OS for those of you who want to go it alone or are just interested.
Firstly, why all the fuss about LCDs? Although they're reducing in price from month to month, TFT monitor supply will reportedly struggle to match demand in 2004, which may slow further price reductions. LCD monitors work by using a fine grid of pixels and also use less energy than CRT monitors. Their thin design means they use less space than CRT monitors and weigh much less too. Generally, LCD monitors have a sharper image that's flicker free, which is nicer to work with. CRT monitors, on the other hand, are cheaper and so higher resolutions can be afforded. CRTs also 'react' faster to changes in the displayed image, whereas LCDs tend to update slower (response time is generally in the order of tens of milliseconds).
A Monitor Definition File defines the characteristics of a display and the various resolutions it can handle. RISC OS needs an MDF to tell it how best to use a monitor without damaging it, although modern LCD monitors will refuse to display a resolution that it can't handle. Fortunately, there's various ways to find a suitable MDF. You can generate your own using Acorn's MakeModes software provided you're competent with MakeModes and aware of your monitor's specification. Alternatively, you can have your supplier produce an MDF for you if possible. Another method is to use an existing MDF file for a CRT monitor that matches the resolutions provided by your LCD monitor. For example, my RiscPC's 15" LCD monitor works well with the MDF for the Iiyama Vision Master Pro 450. Modern LCD monitors also have an 'auto-adjust' button or on-screen menu option that automatically adjusts the monitor to match the computer's video output, which helps. You can find a load of MDFs from here. However, for top end screen resolutions, a properly defined MDF is preferred. Additionally, the software with the Viewfinder graphics card can generate a suitable MDF for a monitor if you can provide the monitor's specifications.
Another tip, if you're having trouble, is to change
*configure sync to 0 or 1, if the 'auto' setting doesn't work.
"We supply a custom designed MDF with each of our LCDs," explained CJEMicros' Chris Evans. "Some monitors (LCD or CRT) will not display until an MDF is loaded. I made a newsgroup posting about it some time ago [with the] subject 'when is Mode 27 not the same as Mode 27'."
The setup of an LCD monitor can be a fiddly process but there is help as Peter Gaunt's Zebra software can be used to calibrate an LCD monitor. While Zebra displays a test pattern, the LCD monitor's previously mentioned 'auto-adjust' feature can be activated. The monitor will then use the test pattern to ensure the display's positioning, colour balance and synchronisation timings are spot on.
Check the maximum resolution of the LCD monitor before purchase to make sure you're truly happy with it. I personally use my RiscPC in 1024x768 in 32K colours at 70Hz on a 15" TFT monitor (pictured), which is possible with the RiscPC's 2MB VRAM although that might be woefully tiny for some users. Obviously if you're using a RISC OS computer that provides much greater resolutions (namely a Viewfinder, Omega, Iyonix or otherwise), you'll probably want a monitor that can take advantage of large desktops and high refresh rates available to you - LCD monitors capable of 1600x1200 aren't exactly cheap. Also, be aware that some larger LCD monitors have a maximum resolution of 1280x1024, which is an X:Y aspect ratio of 5:4. Screen resolutions of 800x600 and 1024x768 have a ratio of 4:3 and displaying them on a 5:4 screen will result in a stretched image, unless the LCD monitor provides the ability to control this scaling.
Due to their inherent complexity, LCD monitors aren't perfect and there's a chance there may be a few defective pixels on the screen. If you're lucky you won't notice any, but once you do, you usually can't help but be distracted by them. Different manufacturers and suppliers will have different pixel defect tolerances, which defines how many defective pixels a monitor can have before it can be returned for a replacement unit - check this tolerance before purchase.
LCD monitors use standard 15-pin VGA video connectors. Paul Richardson of Explan also commented: "There is a better RISC OS video output system developed by Pace engineers, which would operate with DVI graphics cards. I assume this design work has passed to Castle along with the rest of RISC OS, since any work by Pace engineers had to be added back into the source-pool. However, it's possible that Castle don't realise what they've got, or are unaware of how important this code is for the future types of digitally-driven monitors."
CJEMicros, Liquid Silicon, Explan websites - dealers who know a thing or two about LCD monitors and RISC OS
Also, LCD pros and cons and how to pick an LCD
How TFT LCD monitors work
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