7.9 The HD Parallel Interface

This obsolescent interface is suitable for RGB or colour difference working. In RGB, each component is carried on three separate sets of conductors whereas in colour difference working the luma is carried on one set and the two colour difference signals are multiplexed into two of the conductor sets, the third being unused, although an auxiliary signal such as a key channel may optionally be sent on the third set. The general concept is identical to the SD parallel interface, with one differential pair of wires per bit and a single differential clock, all at 110 ohm ECL levels. Each pair has its own screen and so three connector pins are required for each bit. Given that three sets of ten-bit data plus a clock are needed, it is clear that the connector will need a massive 93 pins. At a clock rate of 74.25 MHz, this interface is restricted to a length of 20 metres.

As this interface is essentially two, or three for RGB, channels in parallel, each channel has its own synchronizing means. Thus the luma data have their own TRS-ID and the colour difference data also have their own TRS-ID. The TRS codes in each channel should be co-timed.