Transition-Minimized Differential Signaling (TMDS)

DVI makes use of Transition-Minimized Differential Signaling (TMDS) wherein eight bits of video data are converted to a 10-bit transition-minimized, DC-balanced value.  This value is then serialized and sent to the receiver where the data is de-serialized and converted back to eight bits.

The three TMDS signals needed for RGB make up one TMDS link.  A DVI connector can carry up to two TMDS links providing for better resolutions and timing requirements.  Single TMDS link DVI cables can support resolutions and timings that use a video clock rate of about 25-165 MHz.

The following resolutions and timings are supported by a single link DVI cable:

  • SXGA resolution (1280 x 1024) with 85-Hz refresh rate
  • UXGA resolution (1600 x 1200) with 60-Hz refresh rate
  • SDTV resolutions of 480i, 480p, 576i and 576p
  • HDTV resolutions of 720p and 1080i

Video clock rates of 165-330 MHz on the other hand, are supported only by dual TMDS link DVI cables. With dual link DVI cables, however, each TMDS link operates at only one-half the frequency of single link DVI. So the clock and bandwidth is shared by these two links.