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SFH7773 Datasheet(PDF) 9 Page - OSRAM GmbH |
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SFH7773 Datasheet(HTML) 9 Page - OSRAM GmbH |
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9 / 23 page  register for the ALS (0x80). Each command needs to be acknowledged by the slave. After activation the master ends the communication with a STOP command “P” (SDA line is changing from LOW to HIGH during SCL line stays HIGH). In this example the measurement interval time is kept at the default value (500 ms). 2. Activation of the PS: For the activation of the PS sensor the master needs to write the activation command (0x03) into the corresponding control register (0x81). By writing 0x1E into the I_LED register (0x82) the LED current is set to 200 mA. The measurement interval is left at the default value (100 ms). After activation the master ends the communication with a STOP command. 3. Wait time: After activation, the sensor will change from STAND-BY to FREE-RUNNING mode. After a delay of 100 ms for ALS / 10 ms for PS the first measurement value is available and can be read via the I²C-bus. 4. PS value: reading data The PS value is accessible via the output register (0x8F). After reading the 8-bit word, the communication can be ended by the master with a not acknowledge “NA” and the stop command “P”. The PS output reading of the SFH 7773 can then be converted from hexadecimal to decimal. 5. ALS value: reading data (LSB and MSB) The sensor’s 16bit ALS measurement value is composed of 2 bytes (LSB & MSB). The bytes are accessible via the two output registers (0x8C, 0x8D). After addressing the LSB (least significant byte) resp. the MSB (most significant byte) output register, the communication direction has got to be changed from the slave to the master by repeating the address and the R/W byte with a changed R/W bit. After reading LSB and MSB, the communication is ended by the master with a not acknowledge “NA” and the stop condition “P”. The conversion of the ALS output data of the SFH 7773 from hexadecimal to decimal can easily be calculated: Fig. 15: Combined mode structure. ALS_DATA_LSB = F0 (1111 0000) ALS_DATA_MSB = 83 (1000 0011) Final result (hexadecimal): 83 F0 counts Final result (decimal): 33776 counts, which correspond to around 30.4 klx (based on a conversion factor of typ. 0.9 lux/count). After finishing the measurement, the SFH 7773 mode may be changed to STAND-BY via the control register. Combined mode To ensure interference free communication the I²C-bus combined mode should be used. Instead of performing two independent read or write commands (COM 1 & COM 2) the commands can be combined by a repeated start condition “Sr” (Fig. 15 illustrates the combined mode structure). The start and repeated start commands (“Sr”) are the same: the SDA line is changing from “1” to “0” during SCL line “1”. The “Sr” condition is placed behind “A” or “NA”. The combined mode is not limited to 2 read/write commands, so the addressing of the sensor and reading/writing of multiple register values can be performed within one block. Block read mode The Block read mode of the SFH 7773 can be used to read all output registers in cyclic manner. December 12, 2011 page 9 of 23 |
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