Touch standard aims to replace proprietary interfaces

Article By : Rick Merritt

MIPI Touch aims to simplify work for engineers who currently support a handful of proprietary approaches.

The MIPI Alliance has started work on a standard interface for touch screens using its emerging I3C interconnect announced earlier this year. MIPI Touch, described at a developer’s conference in California, aims to simplify work for engineers who currently support a handful of proprietary approaches.

The interface includes a standard command set for relaying messages between the application processor and other touch components. It aims to replace a variety of approaches using I2C and SPI links the group claims are not well optimised for mobile systems.

The spec, now in a draft to contributors, is expected to be ratified sometime next year. It is being developed by companies including Intel, NXP, Qualcomm, Samsung and Synaptics.

It’s not clear if potential users such as Apple and their vendors will support the effort. In the iPhone 6, Apple used a touchscreen controller from Broadcom and a line driver from Texas Instruments, according to a teardown by TechInsights. Apple is a contributing member of MIPI, but Broadcom is not a member.

Today’s many touch-based smartphones, tablets and in-car gadgets send data “over a slow interface with customised register sets and functions so every OEM writes special drivers…MIPI Touch makes the process more transparent,” said Dale Stolitzka, a principal engineer in Samsung Display and chair of the MIPI Alliance’s display working group.

[MIPI Touch blockdiagram]
__Figure 1:__ *MIPI Touch will support both standard and custom commands over an I3C interconnect. (Source: MIPI)*

MIPI Touch is not specific to today’s mainstream capacitive touch sensors. It will support single-, multi-touch and stylus inputs; and it allows vendors to create custom commands and functions outside a basic shared command set.

The current version of the spec does not take into account force data, also known as haptics, but the spec could be updated in the future to include it. Earlier this month, Apple described a large custom haptics sensor it built into its iPhone 7.

Engineers may be able to implement MIPI Touch in firmware if their devices have an embedded controller, Stolitzka said. The MIPI I3C interface the touch standard is based on is in a final review stage now. I3C supports data rates of more than 30Mbits/second and has compatibility modes for working with I2C.

“We’re trying to make it as easy as possible for vendors to implement this quickly,” said Stolitzka.

Looking ahead, the rise of virtual and augmented reality goggles are expected to drive needs for new MIPI display interfaces with greater throughput.

“The issue will be how much display area in pixels people need to look at and the commensurate bandwidth to support the resolution demands,” Stolitzka said. “We probably need to think about doubling bandwidth from where we are with the D-PHY interface at about 4Gbits/s today,” an effort that could take about a year, he added.

In addition, MIPI aims to extend its work beyond the smartphone to cars and TVs. That could require extending some interfaces to support distances measured in meters rather than inches, said Rick Wietfeldt, chair of MIPI's technical steering group in a keynote talk.

This article first appeared on EE Times U.S.

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