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Multi-touch Solution for 4-Wire Resistive Touch Panel

Features of Toshiba's Multi-touch Technology

Multi-touch Solution for 4-Wire Resistive Touch Panel

1. Users can use the existing 4-wire resistive panel without size limitation. The system cost can be greatly reduced.

2. The feature of 4-wire resistive panel allows users to use a stylus pen, finger nails or gloves to interact with the panel.

3. One or two touch points can be detected at a time.

4.Two coordinate values can be detected at a time. The two points can be tracked and output separately.

5. Users can select the level of filtering function to prevent malfunction.

6. In a standby state, the controller can achieve low-power consumption mode and can control the bias shutdown of a panel.

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Double-touch recognition on a 4-wire resistive touch panel

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Toshiba's Multi-touch Solution Roadmap

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Series MCU Firmware
Phase Ⅰ
Multi-touch controller
TLCS-870/C1 TMP89FM43KQG-xxxx Under development
TMP89FM46KDUG-xxxx Under development
Phase Ⅱ
General-purpose MCU +
Multi-touch control firmware
TLCS-870/C1 TMP89FM46KDUG Under development
TMP89FW20AUG Under development
TMP89FW24AFG Under development
TX03 TMPM3xxUG Under development
TMPM3xxFG Under development
Phase Ⅲ
Built-in multi-touch interface ASSP
TX03 Under planning Under planning
TX09 TMPA90x Under planning
TMPA91x Under planning

Applicable to all line-up of Toshiba MCU

4-Wire Resistive Multi-touch Panel Solution of Toshiba has three successive phases. In phase 1 controllers dedicated only to the multi-touch control are produced. The controller enables to communicate with a serial interface to a host controller in the system. Next, phase 2 will realize both functions of the multi-touch control and host control in one Toshiba microcontroller. Several kinds of firmware are under development applied to 8bit TLCS870/C1 series and, for more complicated systems, 32bit TX03 series microcontrollers. These microcontrollers integrate AD converters which convert the output voltages from the touch panels, Flash memories which store user application software as well as the firmware which detects and calculates each coordinate of the two touched points.
And in phase 3, multi-touch control by TX09 series ASSPs is under planning. The ASSP devices have been already in mass production stage.

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Toshiba's multi-touch solution for a 4-wire resistive panel

Recently smart phones and tablet terminals have become widespread increasingly. A touch panel is attached on the display of each machine, and data input is done by user touches with fingers or stylus pens on the panel. There are several kinds of thin film touch panels such as capacitive touch panels, resistive ones and so on. Among them, a 4-wire resistive touch panel is one of the most popular panels because of its simple structure and low cost. The 4-wire resistive touch panel has more feature that a touch by a stylus pen, a finger, a nail, or even a gloved finger is available.
Though the touch panel has so many advantages, it can be used only for an application of no more than a single touch. Double touches are necessary when operating enlargement, reduction, and rotation of a picture image on a display, which is beyond the ability of the 4-wire resistive touch panel.
Toshiba, however, has developed a technology to detect two touch points simultaneously on the 4-wire resistive touch panel after its conducting profound researches and analyses. This new technology is firmware solution on a microcontroller.

Toshiba's technology for the multi-touch solution

Before introducing Toshiba's multi-touch solution, single-touch operation on the 4-wire touch panel should be explained.
The panel consists of two transparent resistive thin films which overlap one another with a thin space. The bottom film has terminals at the top edge of the film and at the bottom edge, and the top film has also terminals at the right and the left edges, respectively.
The way how to detect the coordinates of the single touch point is as follows. When some location is touched by a finger on the panel, the top film is bent to connect to the bottom film at that point. Power voltage VDD and GND are supplied to the top edge terminal and bottom one on the bottom film, respectively, which gives a voltage value on the touched point on the bottom film. The voltage is transferred to the top film’s terminal through the touched point and is eventually converted to Y coordinate in a controller.
By the same way X coordinate of the touched point is acquired by the voltage value on one of the terminals of the bottom film through the touched point, and the left and right edge terminals of the top film are supplied with VDD and GND, respectively.
These twice measurements identify directly the coordinates of the touched point.

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Now let's consider the case of simultaneous double touches. The big difference between the double touches and the single one is that the former touches generate a current flow between the touched points on both the bottom and top films, on the other hand, the latter, no current at all.
When, for example, VDD and GND are supplied to the terminals on the bottom film, the monitor voltage on one of the terminals on the top film does not represent the coordinates of the two touched points, because the voltage will be one of the intermediate values between the voltage of one touch point and that of the other's.
Toshiba has focused to solve the problem. Simulation results have been verified by experiments again and again, and eventually a very effective calculation method has been found. Toshiba has succeeded to make the solution into a firmware IP in Toshiba microcontrollers to pick up the two coordinates in real time.

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