MSP430 programming for serial interfacing with sensors

Network and Systems Laboratorynslab.ee.ntu.edu.tw

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SPIMaster–Slave modeSynchronous protocolAll transmissions are referenced to a common clockClock generated by the master (MCU)Four main signalsMaster Out Slave In (MOSI): data from master to slaveMaster In Slave Out (MISO): data from slave to masterSerial Clock (SCLK or SCK): clockChip Select (CS): select particular peripheral when

multiple peripherals are connected to master


SHT11Relative humidity and temperature sensors Digital output Manufacturer defined interface

two wires bi-direction

1. Use a GPIO pin as clock (SCK), it is always output direction

2. Use another GPIO as DATA, dynamic setting it to input(read) or output(write) direction


Taroko Connections


Start Transmission and Send CommandHow to start

What are the commands available


An Example: SHT11Timing diagram

Pull-up

Data pin in output

direction

Set data pin to input direction,

then SHT11 controls the DATA line


Software Implementation


Convert to Physical Values 12-bit humidity, 14-bit temperatureTemperature

Humidity


Device DriverDownload here

http://nslab.ee.ntu.edu.tw/courses/wsn-labs-spring-09/labs/sht11Driver.rar

Important functions in SHT1x_sensirion.cvoid sht1xInit();void sht1xReset();char sht1xMeasure(unsigned char *p_value,

unsigned char *p_checksum, unsigned char mode);

void sht1xCalculate(float *p_humidity ,float *p_temperature);


Functionschar sht1xMeasure(unsigned char *p_value, unsigned

char *p_checksum, unsigned char mode);mode: { TEMP, HUMI }Store measured value to *p_valueStore 8-CRC checksum to *p_checksumvoid sht1xCalculate(float *p_humidity ,float

*p_temperature);Convert measured value to physical valuePut the measured value in *p_humidity, *p_temperatureResult will also place in *p_humidity, *p_temperature

(overwrite)


Example

MSP430 programming for serial interfacing with sensors

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