Abstract: Cypress TrueTouch™ capacitive touchscreen solutions have wide applications in multiple fields: single-point touch, multi-point touch gestures, and multi-point touch location recognition. The TrueTouch™ chip communicates with the host via TX/I2C/SPI/USB interfaces. PSoC Designer 5.0 provides various corresponding communication user modules, which greatly simplifies programming and debugging. This article discusses and compares the characteristics of various communication user modules, helping users choose the appropriate method for specific applications. With the popularization of portable electronic products such as mobile phones and PDAs, there is a demand for smaller product sizes and larger LCD displays. Limited by overall weight and mechanical design, human-machine interface (HMI) has begun to transition from traditional mechanical buttons to resistive touchscreens. The iPhone's release in 2007 and its huge success, with its capacitive touchscreen offering higher light transmittance and novel multi-point touch functionality, has become a new hot topic in portable products and shows a trend towards becoming the mainstream input interface method. I. Introduction to Cypress TrueTouch™ Capacitive Touchscreen Solution Cypress PSoC technology integrates programmable analog/digital resources onto a single chip, providing the TrueTouch™ solution for capacitive touchscreens. It covers the entire spectrum from single-touch and multi-touch gesture recognition to multi-touch location recognition. Coupled with the efficient and flexible PSoC Designer 5.0 development environment, the Cypress TrueTouch™ solution is gaining widespread application in the industry. Figure 1 shows a commonly used axis-coordinate sensing unit matrix in the Cypress TrueTouch™ solution. Similar to a touchpad, individual ITO sensing units are connected in series to form a sensing unit along the Y-axis or X-axis. Row sensing units form the Y-axis, and column sensing units form the X-axis, with rows and columns on separate layers. The multi-touch location recognition method is based on mutual capacitance touch detection (a drive excitation signal is applied to the row units, and sensing occurs on the column units; unlike the excitation and sensing methods, this is a self-capacitance method using the same sensing unit). This method can be applied to the detection of any touch gesture, including recognizing the location of all 10 fingers simultaneously (Figure 2). It completely eliminates "ghost points" through mutual capacitance detection. When there are multiple touch points, capacitance change is only detected when the row sensing unit of a certain touch point is driven and the column sensing unit is detected. This allows for the detection of the absolute position of touch points at the intersection of multiple rows/columns. Figure 1 shows the graph of the axis coordinate sensing unit matrix. Figure 2 shows the position of five finger touch points simultaneously. Figure 3 shows different application areas of the Cypress TrueTouch™ solution, including touch buttons, two-finger gesture operations for images, and simultaneous recognition of multi-touch positions and control of multiple targets. Figure 3 shows the Cypress TrueTouch™ capacitive touchscreen solution . II. Communication Interface of Cypress TrueTouch™ Capacitive Touchscreen The Cypress TrueTouch™ capacitive touchscreen mainly communicates with the host via TX/I2C/SPI/USB. The TrueTouch™ chip can directly report some basic gestures (such as two-point touch translation/zoom/rotation) and can also provide a dedicated API to the user. After obtaining the multi-point coordinates, the user can use the API to calculate and recognize more or custom gestures. The API is written in standard C and can run on multiple platforms such as 51/ARM, greatly simplifying the workload of user-side software development. 1. TX Communication Interface: Cypress Designer 5.0 provides the TX8SW user module, which can implement a 7/8-bit RS-232 format software serial interface, supporting transmission speeds of 115200, 57600, 38400, 19200, 9600, 4800, 2400, and 1200 bps. Users can configure the corresponding I/O ports, baud rates, polarities, and stop bits in the code. The TX8SW interface does not occupy the PSoC's digital/analog module resources and provides a unidirectional communication connection from the PSoC to the host. 2. I2C Communication Interface Cypress Designer 5.0 provides several user modules for I2C communication, including I2CHW (allows multi-master communication, can be configured as master or slave, supports 7-bit/10-bit addressing modes), EzI2Cs (operates in slave mode, consuming minimal ROM/RAM resources), I2Cm (operates in master mode), and I2Cs (operates in slave mode). These I2C modules are compatible with Philips' industry-standard I2C bus interface and do not consume PSoC's digital/analog module resources, providing a bidirectional communication connection from PSoC to the host at 100 kbps/400 kbps. When the PSoC communicates with the host via I2C, it typically reports an interrupt to the host via a GPIO after all row/column sensor touch detections are completed. The host responds to the interrupt and reads the required data. The following method can ensure the integrity of the data read by the host: While (1) { TSX_ScanAllSensors(); // TSX is the Cypress mutual capacitance detection user module TSX_UpdateAllBaselines(); // Update the baseline of the sensing unit TSX_GetCentroids(); // Get the position of multiple points TSX_ReportINTwithOvertime(); // Report the interrupt to the host, with timeout control // Detect the RAM read/write counter of the EzI2Cs user module and wait until the host reads all the data while (EzI2Cs_bRAM_RWcntr != sizeof(I2Cregs)) {}; …; // Run other user code } After the host writes predefined data to a specific byte of the I2C Structure, it can notify the PSoC to enter standby mode (periodic working mode + periodic sleep mode) or complete sleep mode. In standby mode, the host PSoC can enter sleep mode. The PSoC periodically wakes itself up using a Sleep Timer to enter a periodic operating mode, detecting certain sensing units (such as scan-only units) to determine if a user activation event has occurred. If an activation event is detected, an interrupt wakes the host and the PSoC enters operating mode; otherwise, it sleeps again and periodically wakes itself up to reduce power consumption. The actual current consumption is a time-weighted average of the operating mode and sleep mode. For example, if the PSoC wakes up 4 times in one second to enter operating mode for detection, each detection lasting 16ms @ 3.2mA, and the rest of the time it enters sleep mode @ 3uA, the actual current consumption = (16ms * 4 * 3.2mA + (1000ms – 16ms * 4) * 3uA) / 1000ms ~ = 0.208 mA. In PSoC Sleep mode, Analog/Digital UM is disabled, preventing all GPIOs from forming current paths. External interrupt wake-up of I2C communication pins is enabled, and then it enters Sleep mode. The host can then wake up the PSoC by calling an I2C read or write event. 3. SPI Communication Interface Cypress Designer 5.0 provides SPIM (set to master mode) and SPIS (set to slave mode) UM. They use Tx Buffer/Rx Buffer, Control/Shift registers, and Digital communication modules to implement 8-bit full-duplex synchronous communication. Users can select the SCLK (generated by the SPI master to set the communication bps) frequency and polarity, LSB First, and other attributes to support SPI modes 0, 1, 2, and 3 (see Table 1). Table 1: SPI Mode Selection 4. USB Communication Interface Cypress Designer 5.0 provides USBUART (using the USB interface to simulate a COM port) and USBFS UM. USBUART is as convenient to use as a serial port on both the PSoC and PC. After setting parameters such as VendorID, ProductID, VendorString, ProductString, SerialNumberType, SerialNumberString, DevicePower, and MaxPower, the compiled project automatically generates an INF file. When the PSoC is connected to the PC, the PC installs this INF file, enabling bidirectional communication between the two. USBFS supports Control, Interrupt, Bulk, and Isochronous transfers, providing a low-level driver mode for USB IN/OUT control nodes, interpreting requests from the USB Host, and assigning them to the appropriate functions. The USBFS Setup Wizard makes it easy to configure device descriptors, and users can also configure the USB as an HID (Human Interface Device) device or a general-purpose USB device. Neither USBUART nor USBFS interfaces consume PSoC's digital/analog module resources, providing a USBFull Speed ​​bidirectional connection from the PSoC to the host. III. Choosing Different Communication Interfaces for Cypress TrueTouch™ Capacitive Touchscreens When selecting a Cypress TrueTouch™ touchscreen solution, the communication interface can be flexibly selected according to the specific application requirements (see Table 2): The advantages of capacitive touchscreens are widely recognized, with their enhanced durability and elegant human-machine interface providing consumers with a brand-new operating experience. As the capacitive touchscreen market gradually expands, flexible communication interface selection will help Cypress TrueTouch™ capacitive touchscreen solutions better serve users.