Bi-directional data transfer using two pair of differential lines as a single additional differential pair

Abstract

Data is transferred from a processor to a display in one direction. However, there are many reasons for data to be transferred in both directions along a cable connecting the processor and display. This invention describes a method of sending data from the display back to the processor computer in a situation in which the video data transferred to the display is in digital form. Differential wire pairs are used to transmit red, green and blue digital pixel data in a first direction from the processor to the display using a high common mode rejection ratio in each of the twisted wire differential pairs. Using this common mode, digital data may be serially transmitted in a reverse direction from the display. The common mode is offset between two of the twisted wire differential pairs by varying the DC offset or reference voltage in one of the twisted wire differential pairs relative to the other differential pair. Both wires in a pair have their DC offset adjusted to as not to affect digital pixel data transmitted in a forward direction. DC offsets in each pair are compared, with a change in DC offset of one pair used for transmitting a logic high and a change in the DC offset of the other pair used for transmitting a logic low. In this way, bidirectional data transfer is accomplished without increasing the number of twisted wire pairs coupled between the processor and display.

Dependencies are inferred from the claim text.