Electrical Interface
Originally, both electrical and optical interfaces were defined by SMPTE, over concerns that an electrical interface at that bitrate would be expensive or unreliable, and that an optical interface would be necessary. Such fears have not been realized, and the optical interfaces are seldom if ever used, and are likely to be deprecated in future revisions of the standard.
The cabling used for the SMPTE 292M electrical interface is coaxial cable with a nominal impedance of 75 Ω. Data is encoded in NRZ format, and a linear feedback shift register is used to scramble the data to reduce the likelihood that long strings of zeroes or ones will be present on the interface. The interface is self-clocking. Framing is done by detection of a special synchronization pattern, which appears on the (unscrambled) serial digital signal to be a sequence of twenty ones followed by forty zeroes; this bit pattern is not legal anywhere else within the data payload.
The SMPTE 292M digital interface is known to be reliable (without use of repeaters) at cable lengths of 100 m or greater.
Read more about this topic: SMPTE 292M, Technical Details
Famous quotes containing the word electrical:
“Few speeches which have produced an electrical effect on an audience can bear the colourless photography of a printed record.”
—Archibald Philip Primrose, 5th Earl Rosebery (1847–1929)