Transition Minimized Differential Signaling
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Transition Minimized Differential Signaling, or TMDS, is a technology for transmitting high-speed serial data. TMDS is the technology used by the Digital Visual Interface which is used to digitally send graphics data to modern digitally interfaced display monitors. The transmitter incorporates an advanced coding algorithm which has reduced electromagnetic interference over copper cables and enables robust clock recovery at the receiver to achieve high skew tolerance for driving longer cable lengths as well as shorter low cost cables.
TMDS was developed by Silicon Image, Inc. as a member of the Digital Display Working Group.
The encoding works on eight bits at a time in two stages, resulting in ten bits. In the first, each bit is either XOR or XNOR transformed against the previous bit, although the first bit is not transformed at all. The system chooses between XOR and XNOR by determining which will result in the fewest transitions, and a ninth bit is added to show which was used. In the second stage, all nine bits are optionally inverted to even out the balance of ones and zeroes and therefore the overall DC level. A tenth bit is added to indicate whether the inversion took place.