 | This article relies largely or entirely on a single source. (April 2023) |
ITU-R Recommendation BT.656, sometimes also called ITU656, is a simple digital video protocol for streaming uncompressed PAL or NTSC standard-definition television (625 or 525 lines) signals. The protocol builds upon the 4:2:2 digital video encoding parameters defined in ITU-R Recommendation BT.601, which provides interlaced video data, streaming each field separately, and uses the YCbCr color space and a 13.5 MHz sampling frequency for pixels.[1]
The standard can be implemented to transmit either 8-bit values (the standard in consumer electronics) or 10-bit values (sometimes used in studio environments). Both a parallel and a serial transmission format are defined. For the parallel format, a 25-pin D-Sub connector pinout and ECL logic levels are defined. The serial format can be transmitted over 75-ohm coaxial cable with BNC connectors, but there is also a fibre-optical version defined.
The parallel version of the ITU-R BT.656 protocol is also used in many TV sets between chips using CMOS logic levels. Typical applications include the interface between a PAL/NTSC decoder chip and a DAC integrated circuit for driving a CRT in a TV set.