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QST108 数据表(PDF) 17 Page - STMicroelectronics |
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QST108 数据表(HTML) 17 Page - STMicroelectronics |
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17 / 38 page ![]() QST108 Device operating modes 17/38 4.5.3 IRQ pin The IRQ pin is an open drain output with an internal pull-up. This pin (available in I2C mode only) can be used to inform the Master device about any change in the key status. The IRQ line is pulled low every time the state of any of the enabled keys changes. This includes any change in the touch state of the key or faulty key. The reported changes may then be accessed by the Master device by using the GET_KEY_STATE command. To improve communication response time, this signal suspends Low Power mode until the Master device has issued a communication with the QST device. 4.5.4 Communication packet The communication between the Master device and the QST108 (Slave) consists of two standard I2C frames. The first frame is sent by the Master device using the QST108 device address with the write bit set. The data bytes consist of the command byte which is eventually followed by the parameters and a checksum byte. The second one is sent by the Master device using the QST108 device address with the write bit reset. The QST108 complete the frame with data according to the command previously sent by the Master device. The device finishes the frame by sending a checksum byte for communication integrity verification. The QST108 slave address is programmable using the option resistors mapped on pins OPT2 to OPT4 (see Table 9). If the read frame is omitted, the command may not be taken into account. To initiate the communicate with the QST108, the Master device must send the GET_DEVICE_INFO command in order to unlock access to all the other commands. Table 9. I²C address versus option resistor Option configuration I2C Address OPT4 OPT3 OPT2 ADD[6:3] ADD2 ADD1 ADD0 Hex value VSS VSS VSS 0101 0 0 0 0x48 VSS VSS VDD 0 0 1 0x49 VSS VDD VSS 0 1 0 0x4A VSS VDD VDD 0 1 1 0x4B VDD VSS VSS 1 0 0 0x4C VDD VSS VDD 1 0 1 0x4D VDD VDD VSS 1 1 0 0x4E VDD VDD VDD 1 1 1 0x4F |
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