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Should I use a passive Display Splitter to use Dual Display from a Single Port?

Article ID: 46
Last updated: 13 Jun, 2013
Article ID: 46
Last updated: 13 Jun, 2013
Revision: 8
Views: 2679
Posted: 08 May, 2013
by Tim Rafferty
Updated: 13 Jun, 2013
by Andrew Sharrad

Problem

A common scenario is the need to give a cloned output to more than one monitor and/or projector at the same time. For example, you may have a monitor already connected but then need to connect a projector.

One solution available on the market is the passive video splitter. A passive splitter has no power supply and no electronics. It is simply wired to duplicate the signals to two HDMI, DVI or VGA connectors.

The use of passive video splitters, such as a passive VGA splitter (15-pin) can cause configuration and reliability issues with modern PC systems and therefore is not recommended.

Issue 1: Mismatched display settings

Using a physical clone of a display prevents the PC from being configured to support the different output device's characteristics, such as resolution. This means that the output has to be configured to the lowest common denominator of the two in both the X and Y axis. For example:

Monitor 1: 1366x768

Projector: 1280x1024

Common denominator: 1280x768 - this is not the ideal resolution for either device and will give a stretched, distorted or letter box display on one or more device.

Solution: Use seperate physical output ports on your system. Windows will automatically adjust the output for the best possible display on a cloned setup. Or, using the seperate output ports, configure a spanned desktop. This will allow you to run each device in its native resolution, and will allow you to drag and drop application windows between the two screens.

Issue 2: DDC Pins shorted - display not configured correctly; damage may occur

Most interfaces (including VGA 15-pin, DVI, HDMI and Display Port) may use of a communications channel called DDC.

This is a communication channel from the monitor or projector back to the PC. This carries configuration information such as PNP ID, native resolution etc.

Shorting the DDC information together by physically connecting the two outputs from two devices together can damage the device and the PC host system.

Solution: Use seperate physical display outputs from the PC will ensure DDC information correctly gets back to the host PC system. If you do use a passive splitter - and this cannot be recommended - ensure that the DDC pin from one of the outputs is disconnected (for example, VGA pin 12 from one of the output devices).

Issue 3 - Manual Configuration required

Because a passive physical splitter cannot handle DDC information for both devices correctly, Windows may not be automatically able to determine the correct output resolution. The user will need to manually configure the correct resolution every time the device is connected. If a second device is connected while the system is running, the user may need to manually adjust the resolution on the original device to bring the resolution down to an acceptable setting for the new device.

Solution: Use seperate physical display outputs from the PC

Other Issues

Other issues related to the use of passive splitters include problems where projectors may not display a signal unless the PC is powered up first. This again relates to DDC handshaking. Use seperate physical display outputs.

Please contact your account manager if you would like to discuss upgrade options to your system to support multiple outputs. A system that supports multiple outputs resolves the problems listed above as well as giving control over which output is the primary and which output is the secondary, in the case of a spanned desktop.

Applies to:

  • All systems including PCs and laptops, with or without a dedicated graphics card.

This article was:  
Article ID: 46
Last updated: 13 Jun, 2013
Revision: 8
Views: 2679
Posted: 08 May, 2013 by Tim Rafferty
Updated: 13 Jun, 2013 by Andrew Sharrad
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