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công cụ tìm kiếm bảng dữ liệu linh kiện điện tử |
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công cụ tìm kiếm bảng dữ liệu linh kiện điện tử |
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STS21 bảng dữ liệu(PDF) 6 Page - List of Unclassifed Manufacturers |
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STS21 bảng dữ liệu(HTML) 6 Page - List of Unclassifed Manufacturers |
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6 / 12 page  Datasheet STS21 www.sensirion.com Version 2 – December 2011 6/12 Parameter min typ max Units SCL frequency, fSCL 0 - 0.4 MHz SCL High Time, tSCLH 0.6 - - µs SCL Low Time, tSCLL 1.3 - - µs SDA Set-Up Time, tSU 100 - - ns SDA Hold Time, tHD 0 - 900 ns SDA Valid Time, tVD 0 - 400 ns SCL/SDA Fall Time, tF 0 - 100 ns SCL/SDA Rise Time, tR 0 - 300 ns Capacitive Load on Bus Line, CB 0 - 400 pF Table 5 Timing specifications of digital input/output pads for I2C fast mode. Entities are displayed in Figure 9. VDD = 2.1V to 3.6V, T = -40°C to 125°C, unless otherwise noted. For further information regarding timing, please refer to http://www.standardics.nxp.com/support/i2c/. 5 Communication with Sensor STS21 communicates with I2C protocol. For information on I2C beyond the information in the following Sections please refer to the following website: http://www.standardics.nxp.com/support/i2c/. Please note that all sensors are set to the same I2C address, as defined in Section 5.3. 8 Furthermore, please note, that Sensirion provides an exemplary sample code for SHT21 sensors on its home page – compare www.sensirion.com/SHT21. This sample code can be used for STS21 sensors with minor adjustments (I2C address, no RH measurement). 5.1 Start Up Sensor As a first step, the sensor is powered up to the chosen supply voltage VDD (between 2.1V and 3.6V). After power-up, the sensor needs at most 15ms, while SCL is high, for reaching idle state, i.e. to be ready accepting commands from the master (MCU). Current consumption during start up is 350µA maximum. Whenever the sensor is powered up, but not performing a measurement or communicating, it is automatically in sleep mode (idle state). 5.2 Start / Stop Sequence Each transmission sequence begins with Start condition (S) and ends with Stop condition (P) as displayed in Figure 10 and Figure 11. 8 For sensors with alternative I2C address please contact Sensirion via info@sensirion.com. Figure 10 Transmission Start condition (S) - a high to low transition on the SDA line while SCL is high. The Start condition is a unique state on the bus created by the master, indicating to the slaves the beginning of a transmission sequence (bus is considered busy after a Start). Figure 11 Transmission Stop condition (P) - a low to high transition on the SDA line while SCL is high. The Stop condition is a unique state on the bus created by the master, indicating to the slaves the end of a transmission sequence (bus is considered free after a Stop). 5.3 Sending a Command After sending the Start condition, the subsequent I2C header consists of the 7-bit I2C device address „1001‟010‟ and an SDA direction bit (Read R: „1‟, Write W: „0‟). The sensor indicates the proper reception of a byte by pulling the SDA pin low (ACK bit) after the falling edge of the 8th SCL clock. After the issue of a measurement command, the MCU must wait for the measurement to complete. The basic commands are summarized in Table 6. Hold master or no hold master modes are explained in the next Section. Command Comment Code Trigger T measurement hold master 1110‟0011 Trigger T measurement no hold master 1111‟0011 Write user register 1110‟0110 Read user register 1110‟0111 Soft reset 1111‟1110 Table 6 Basic command set, T stands for temperature 5.4 Hold / No Hold Master Mode There are two different operation modes to communicate with the sensor: Hold Master mode or No Hold Master mode. In the first case the SCL line is blocked (controlled by sensor) during measurement process while in the latter case the SCL line remains open for other communication while the sensor is processing the measurement. No hold master mode allows for processing other I2C communication tasks on a bus while the sensor is measuring. A communication sequence of the two modes is displayed in Figure 12 and Figure 13, respectively. SDA SCL 70% 30% 70% 30% SDA SCL 70% 30% 70% 30% |
Số phần tương tự - STS21 |
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Mô tả tương tự - STS21 |
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