by Oleg Artamonov
06/13/2007 | 10:39 AM
USB connectors appeared on computer monitors far back during the reign of CRT models. They played a secondary role, though, usually servicing the monitor’s integrated USB hub. The hub was often passive, without additional power, and had nothing to do with the monitor’s own electronics. You might as well buy a separate hub and place it next to the monitor. Monitors that could be set up from the PC were an example of a deeper integration of the USB interface, but they soon disappeared due to the arrival of DDC/CI (Display Data Channel / Command Interface) that allowed controlling the monitor via software without an additional USB connection.
However, there is no fundamental limitation to transferring video via the USB. Yes, the bandwidth of USB 2.0 (480Mbps) is only sufficient for transferring non-compressed video with a resolution of 640x480 and a frame rate of 60Hz, but why should the video stream not be compressed? There have long been programs for controlling a PC remotely that can transfer the image not only via Ethernet networks but even via ordinary modems. Yes, they can only transfer the elements of the standard graphical Windows interface (because not the image proper, but GDI commands that construct the image are being transferred, actually), so there is no talking about watching movies or playing games, but the fact that graphical information can be transmitted across low-speed networks cannot be denied.
So, the problem is not about the bandwidth of the USB interface, but about a chip that would decode a video stream compressed to such a level as to fit into the available bandwidth.
DisplayLink, formerly Newnham Research, took to developing such chips some time ago. Right now they offer two chips, DL-120 and DL-160:
These chips can receive a compressed video stream via such interfaces as USB, Ethernet or WiMedia (a wireless data-transfer standard with a throughput up to 480Mbps), uncompress it into video with a resolution up to 1400x1050 (DL-120) or 1600x1200 (DL-160) and in full 24-bit color, and output it in RGB (for an analog connection to a monitor) or LVDS (for a digital connection) formats.
The chips use lossless compression, which is expectable. Ordinary video encoding algorithms like MPEG1 or MPEG2 could be used, too, but they work well for movies only. Such algorithms would make a jumble of pixels out of OS and application interfaces with all their thin sharp lines.
The developer’s website doesn’t offer any info about the compression algorithms employed, so we can only make guesses as to the bandwidth it requires and other technicalities. We’ll better talk about a practical implementation of the concept. It is the first monitor with an integrated chip from DisplayLink: the SyncMaster 940UX model from Samsung.
Follow this link to read a description of our testing methodology. The article is called Xbit Labs Presents: LCD Monitors Testing Methodology Indepth.
According to the specification, the SyncMaster 940UX is an ordinary 19” monitor with a TN matrix that is only distinguishable for its high static contrast ratio (the dynamic contrast ratio is specified in the brackets). It’s got a standard native resolution and lacks Response Time Compensation.
Resembling many other Samsung monitors, the 940UX has a good-looking discreetly designed silver-and-black case with a neat round stand. It is a fine example of an unobtrusive, yet tidy and appealing, exterior design.
The monitor is not compact due to the large and wide pole of the stand. This stand provides all the necessary adjustments: tilt, height adjustment, and even portrait mode (although the latter doesn’t work well for TN matrixes: the poor viewing angles of this matrix type become hardly bearable when the screen is turned around by 90 degrees).
Despite the rumors that the 940UX would come with a USB interface only, Samsung didn’t risk such a drastic move. There are both analog and digital video interfaces available. This is expectable, though. As mentioned in the Introduction, the USB-supporting DisplayLink chip is only an addition to the monitor’s electronics, but does not replace it.
The monitor not only uses the USB connection for its own purposes, but has a dual-port USB 2.0 hub, too. Such USB hubs are usually used to connect flash drives and other peripherals, but you may find a very original application for it here: you can connect a second USB monitor to the first one’s port and so on until you run out of the port bandwidth.
A selection of controls typical of Samsung monitors can be found in the bottom right of the front panel. Quick access is provided to the MagicBright modes, to controlling the brightness setting, to the auto-adjustment feature, and to switching between the inputs.
There is a blue LED built into the Power button. It is not very bright and is not distracting at work, but it starts to blink when the monitor slips into sleep mode. And this can be rather irritating at home where the monitor is going to illuminate your room at night with a blinking blue light. Unfortunately, the LED cannot be disabled.
The onscreen menu does not differ from the menus of many other monitors from Samsung. It has a logical structure and is easy to use. Particularly, it remembers the last changed item and shows it the next time you enter the menu.
The monitor offers a set of MagicBright modes with preset contrast/brightness levels and an additional Dynamic Contrast mode available via the same button. In this mode the monitor is automatically adjusting the intensity of its backlight depending on the onscreen image.
The SyncMaster 940UX being an ordinary monitor, but equipped with an additional USB interface chip, it is logical to begin our tests with the same parameters that we study first with all other monitors.
By default, the monitor’s got 100% brightness and 70% contrast. To achieve a 100nit brightness of white we dropped them both to 35%. Brightness is controlled via pulse-width modulation of the power of the backlight lamps at a frequency of 330Hz.
We have no complaints about how the monitor displays color gradients. Its backlight is uniform, too. The vertical viewing angles are rather narrow, but that’s the generic problem of all TN matrixes.
The gamma curves aren’t ideal, yet go close to the theoretical curve. The monitor reproduces the entire range of halftones, without losing details in darks or lights. The gamma curves do not get worse at the reduced brightness/contrast.
The color temperature setup is surprisingly accurate. The difference between the temperatures of different levels of gray is within 500K in the Normal mode. And in the Cool mode, which proves the most problematic one for many monitors, it is only the temperature of the darkest gray that falls out of the otherwise consistent row of values.
The monitor uses ordinary backlight lamps and its color gamut is standard as a consequence. It covers the sRGB color space and even surpasses it in the area of greens.
Lacking a Response Time Compensation mechanism, the 940UX has poor results in the response time tests: an average of 15.6 milliseconds and a maximum of 34.1 milliseconds.
The contrast ratio is quite high, for a TN matrix. The max brightness is normal for an office monitor.
So, the SyncMaster 940UX is a neat and correctly set-up office monitor. It will suit perfectly for working with documents, but its slow matrix is going to disappoint you if you buy it for playing dynamic games.
Having done with the main parameters, let’s now check out the special feature of the 940UX, its USB connection. So, we need a computer with a USB port (any standard USB 2.0 port will do – there are no special requirements to it), Windows XP (the drivers for Vista were under development at the time of our tests; the support for alternative OSes was not even on the agenda), and a powerful enough processor.
The last requirement comes from the fact that the computer’s graphics card cannot output the contents of its frame buffer or anything else into the USB port. It means the monitor driver has to emulate the graphics card on the software level. Thus, it is a purely 2D solution. 3D is not supported since the processor’s capacity wouldn’t be enough to emulate it.
We took a PC with an AMD Athlon 64 3000+ to test the monitor. Not the fastest CPU available today, but quite typical for an office machine, and the SyncMaster 940UX is meant for office use in the first place.
We were somewhat disturbed at finding no driver on the included disc as well as on the Samsung website. It turned out to be simple, though: the driver was stored inside the monitor. The monitor’s USB hub has four ports. Two are wired outside, one serves the DisplayLink chip, and one more is connected to flash memory the driver is stored in. So, as soon as you connect the monitor to a PC, a new removable disk appears in the system. It is identified as a CD-ROM rather than a flash drive, probably to be compatible with Windows’ standard auto-start feature. The driver installer is auto-started from it.
The installation was performed without problems, adding a few new items into the list of devices:
Why two UbiSync monitors? Samsung was kind to offer us two samples of the 940UX so that we could test multi-monitor configurations and the screenshot shows the moment when both monitors are connected (and the second monitor is plugged into the first monitor’s USB hub rather than directly into the computer’s USB port). The third monitor, denoted as “Plug and Play”, is the default monitor of the computer, connected to the graphics card.
Here’s the monitor settings screen in Windows. It shows the default monitor connected to the ordinary graphics card and two Samsung UbiSync monitors connected to the virtual DisplayLink graphics cards.
On the monitor itself the USB input works like the two traditional video inputs. When you switch to the USB input, a standard notification appears for a few seconds.
Everything came to life at the first attempt, in the triple-monitor configuration right away, although this computer, having a GeForce 2 MX card with an analog output only, couldn’t have hoped for such an abundance of display options earlier. Each monitor worked in its native resolution: 1024x768 on the default 15-incher, and 1280x1024 on each 940UX.
What about the CPU load? It was zero when the USB monitors were displaying a static picture. The virtual graphics card’s driver seems to process and transfer data only when the picture on the monitor must be changed.
Nothing changed when we displayed the Windows Task Manager screen with the CPU load graph. The data stream proved to be not intensive enough to load the CPU well. It’s only when we opened up a web-browser on one UbiSync and were scrolling a web-page with text and pictures in it that we managed to get an additional (i.e. additional relative to the same activities as performed on an ordinary, hardware graphics card) CPU load of 30%. A quick scrolling of a web-page is not a very frequent task while the 3000+ CPU is a low-end solution today – so this is quite a good result, we guess.
We also tried to play a movie in a full-screen view. It was not a problem except for additional load on the CPU – it increased to 50% almost. The second monitor, connected to the first monitor’s USB hub, was feeling all right, still displaying a Windows Desktop in its native resolution of 1280x1024, but we didn’t try to launch a second movie on it…
The SyncMaster 940UX is a PC monitor with a USB interface and it really worked via USB in our tests. It cannot replace the traditional D-Sub and DVI interfaces because the software emulation of the graphics card cannot replace the true hardware and because Windows didn’t react normally to our trying to boot up with the USB monitor only (the OS probably found no display to output to until the virtual graphics card’s driver was loaded).
What are possible applications for the 940UX? First of all, it is for people who need to have multiple monitors on their desk but cannot use ordinary models due to technical or cost-related reasons (e.g. if you need to install a lot of graphics cards to have the desired amount of video outputs). The SyncMaster 940UX can be easily connected to any computer with a USB 2.0 port whether it is a notebook, an office computer with an integrated graphics card, or even a more exotic piece of computer hardware.
A special application the 940UX is most appropriate for is the organization of information systems in trade halls, at exhibitions, etc. The USB cord can be quite long (we tested the monitor with a 5-meter cord from a no-name manufacturer and had no problems with it), making it possible to connect half a dozen monitors to a single system case with a modest configuration. If you have to quickly set up a temporary exposition, you can even connect multiple monitors to an ordinary notebook and each monitor will be working individually, in its native resolution, and with perfect image quality.
Here is a photo from CeBIT where this model was first showcased: a row of monitors is connected to a single USB port.
Our tests showed that the CPU load was not too high. Our single-core processor easily coped with a pair of USB monitors. Considering that junior models of dual-core CPUs are as cheap as $60-70 today, the CPU load is not an issue.
On the downside of the USB connection is the total lack of any 3D acceleration (by the way, we wonder how this monitor is going to work under Windows Vista whose interface requires 3D acceleration). However, the target audience of the SyncMaster 940UX consists of people who want a multi-monitor configuration for little money or within technical limitations. Such people are not supposed to be interested in latest 3D games. And when it comes to work only, the SyncMaster 940UX is going to fully satisfy them.