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  • Dave

    Computer Video Signal, Connectors and Cabling Sermon

    There are once again many terms in this sermon so grab the post for this episode so you can get more detail.


    Introduced in 1987, the Video Graphics Array connector (or VGA) is the standard blue 15-pin connector we have all dealt with. It has also been called RGB, D-sub or “that blue cable”. The VGA cable supports resolutions from 640x400 to 2048x1536. With the right equipment, you might be able to pinch a little more res out but that is infrequent. A VGA connection is ANALOG and cable lengths are good up to 25-30 ft.


    You may have heard terms like VGA, SVGA, SXGA, HDTV and WUXGA but these all just define the vector (resolution) of the signal. For PCs, we do not typically use this rating but this comes in to play when looking at projectors given that there native resolution is frequently considered important.


    VGA is to be phased out by 2013 but I am sure support will be around for years after.







    Introduced in 1999, the Digital Visual Interface (or DVI) is the 29-pin connector that came after VGA. It has been called DVI-DVI-D, the “white one” connector or I. This connector is digital, which means that data is transmitted and is not affected by noise or distortion. Something else to consider is that when your display is on its native resolution the DVI the source is based on each pixel on the monitor. When you use a VGA connector, the pixels are not individually lit and the lit pixels are affected by other pixels. For those of you with two monitors, one on VGA and one on DVI, you will notice the DVI looks slight more crisp. This signal is reason behind that. If you have a card that has VGA, DVI and HDMI try to not to use the VGA and get an adapter for the HDMI. You will get better results.


    Now as far as the resolutions for DVI you need to understand single and dual DVI links. Look at your DVI connector and if there are missing pins in the middle then it is a single link DVI cable.


    Just as an FYI, the DVI connector includes pins for analog signal, which is how you can use one of those adapters to go to VGA.


    The highest resolution for a single DVI link is 2098x1311 so when a higher resolution is need the dual DVI link kicks in and you can get that higher resolution. Your video card must support dual link of course and single link is most common.


    There is also Display Data Channel (or DDC or DDC2) on pins six and seven that have information that tells your PC the type of monitor it is. Modern VGA cables also have DDC/DDC2. This ID data is how your PC knows the type and resolution and what drivers to get for your monitors. As a recap, six pins are for data, six pins for analog signal, six pins for data two, five pins for monitor data and six for shield.


    Cable lengths are good to 15 ft at 1080 while you can go longer with lower resolutions or by using a booster.


    DVI is a great connector but since it does not include audio, it is losing out to HDMI.






    BELOW DATA COPIED FROM WIKI at http://en.wikipedia.org/wiki/Digital_Visual_Interface

    • Example display modes (single link):

      • HDTV (1,920 × 1,080) @ 60 Hz with CVT-RB blanking (139 MHz)
      • UXGA (1,600 × 1,200) @ 60 Hz with GTF blanking (161 MHz)
      • WUXGA (1,920 × 1,200) @ 60 Hz with CVT-RB blanking (154 MHz)
      • SXGA (1,280 × 1,024) @ 85 Hz with GTF blanking (159 MHz)
      • WXGA+ (1440 × 900) @ 60 Hz (107 MHz)
      • WQUXGA (3,840 × 2,400) @ 17 Hz (164 MHz)

    • Example display modes (dual link):

      • QXGA (2,048 × 1,536) @ 75 Hz with GTF blanking (2 × 170 MHz)
      • HDTV (1,920 × 1,080) @ 85 Hz with GTF blanking (2 × 126 MHz)
      • WUXGA (1,920 × 1,200) @ 120 Hz with CVT-RB blanking (2 x 154 MHz)
      • WQXGA (2,560 × 1,600) @ 60 Hz with GTF blanking (2 × 174 MHz) (30-inch / 762 mm Apple, Dell, Gateway, HP, NEC, Quinux, and Samsung LCDs)
      • WQXGA (2,560 × 1,600) @ 60 Hz with CVT-RB blanking (2 × 135 MHz) (30-inch / 762 mm Apple, Dell, Gateway, HP, NEC, Quinux, and Samsung LCDs)
      • WQUXGA (3,840 × 2,400) @ 33 Hz with GTF blanking (2 × 159 MHz)



    Introduced in 2003, High-Definition Multimedia Interface (HDMI) is the 19-pin digital connector standard most people tend to favor now. This connector and cable supports any uncompressed video format and carries eight channels of audio. It also can carry Ethernet and a CEC connection which is how your Samsung TV can remote control your Samsung Blu-ray through the HDMI cable. Magic eh? Other names are Aquos Link, Viera Link, Easylink and Bravia Sync.310px-HDMI_Connector_Pinout.svg


    Most of us have the Type A Category 1 connector that we use for our home theater equipment.


    HDMI cables made currently under the 1.3 and 1.4 spec fall under Category 1, which is Standard Speed and Category 2 which is High-Speed. Category 1 cable is fine for most uses but if you are going 3D, cinema 4K, 2160 or 1080p then you want the Category 2.


    Cable length is generally limited to 16 feet (Category 1) but with a higher quality cable (Category 2) you can go to almost 50 feet.


    Also there were specs released with versions 1.2, 1.3 and 1.4 the cables are only different in bit rate. With version 1.4, 3D support was added. It gets hard to weed through the advertised specs (which they are not supposed to advertise anyway) so just get cables that are 1.3 or 1.4 when you buy.


    HDMI also uses the same signal as DVI so no signal conversion is necessary. You just need a simple DVI-HDMI adapter but you lose the audio. This works well, however not all device support HDCP so you may have issues. Check with your manuals for further information on your source device.






    Ah DisplayPort, the cause of this sermon. Introduced by VESA in 2006, DisplayPort is the 20-pin “other” option for video connections. DisplayPort is support by mostly computer and monitor companies so I do think you will be seeing any DisplayPort TVs soon. In fact, DisplayPort was designed to replace both VGA and DVI. Supposedly, Intel, AMD, Dell etc are all going to phase out DVI and VGA by 2015 and just use DisplayPort and HDMI.


    DisplayPort does video and 8 channels of uncompressed audio and transmits in micro data packets. This means the protocol has room for growth for future versions. The DisplayPort signal is NOT compatible with DVI or HDMI which was the topic of the last few BYOB episodes. Dual-link DVI is supported through an active adapter which converts the signal.




    Just to put DisplayPort to bed let’s just say that the people at AMD figured out that DVI was not going to work with easily with three or more monitors so they went with DisplayPort. To keep it simple, the Eyefinity 3 cards usually have four ports, two DVI, one HDMI and a DisplayPort. You could run two monitors on one of these cards with either the two DVIs or a DVI and an HDMI. However, if you want to run THREE monitors the third one must be the DisplayPort stream. The reason for this is complicated and forces me to talk about clocks which will cause my head to explode. Since I do not want to do a sermon on cranial explosions I will forgo the clock sermon and just say that a DVI connection requires one clock where a DisplayPort can share many connections with one clock.


    So where does this leave me? Well I have the XFX 6870 on order. It has Eyefinity and one HDMI, 2 mini DisplayPorts and 2 DVI ports. Since all three of my monitors are DVI then I am screwed right? Well not quite. Since the DisplayPort is the third monitor I would typically need a third monitor with a DisplayPort. Instead though, I bought a PowerColor Active DisplayPort Adapter. This means the video card can output DisplayPort and the adapter will convert it to DVI. This $30 adapter saved me from buying a new monitor just gets DisplayPort. Do not get these adapters mixed up with passive adapters which just convert DisplayPort to DVI but still use the internal clock.


    As I start to feel pressure in my head, specifically my cranial ridge, feel free to check the show notes and visit Tom’s Hardware for a great article by William Van Winkle on why AMD uses DisplayPort at:




    DisplayPort in action. (Only 22”? WTH?? – Martis)




    Benchmarking Notepad and Paint. Misuse of DisplayPort technology!






    Mini-VGA, Mini HDMI, Mini-DVI and Mini DisplayPort


    Additional Resources and Links




    http://en.wikipedia.org/wiki/HDMI Type C






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    I heard in Australia the audio and video HDMI channels are reversed compared to the channels of the audio and video designated channels in the northern hemisphere.
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