Mbed Microcontroller SPI. Spring, 2018 Prof. Jungkeun Park

Transcription

1 Mbed Microcontroller SPI Spring, 2018 Prof. Jungkeun Park

2 SPI Logic Signals Full duplex mode using a master-slave architecture Single master Originates the frame for reading and writing Logic signal Description Output from SCLK Serial Clock Master MOSI Master Out Slave In (Data) Master MISO Master In Slave Out (Data) Slave SS Slave Select (often active low) Master 2

3 Clock Polarity and Phase Conventional names CPOL: clock polarity CPOL = 0: clock idles at 0 CPOL = 1: clock idles at 1 CPHA: clock phase CPHA = 0: in side captures data on the leading edge of the clock CPHA = 1: in side captures data on the trailing edge of the clock Mode numbers SPI Mode Clock Polarity (CPOL/CKP) Clock Phase (CPHA) Clock Edge (CKE/NCPHA)

4 Clock Polarity and Phase Timing diagram 4

5 SPI Port Pins 2 SPIs (mosi, miso, sck) (p5, p6, p7) (p11, p12, p13) CS 는 GPIO 를통해구현 5

6 mbed SPI Module Constructor Constructor SPI(PinName mosi, PinName miso, PinName sclk, PinName ssel = NC) Description mosi: master out / slave in pin miso: master in / slave out pin sclk: clock pin ssel: chip select pin (default: NC) Member functions (selected) Function void format(int bits, int mode = 0) void frequency(int hz = ) int write(int value) Description Configure the data transfer format bits: # of bits per SPI frame (4 ~ 16) mode: clock polarity and phase Set SPI bus clock frequency hz: frequency in hz (default: 1Mhz) Write to SPI slave and return response 6

7 SPI Example Program example Mode 0: clock idle at 0, capture data at leading edge 7

8 SPI Example transmit next bit on falling edge clock idle 8

9 ADXL345 Digital Accelerometer Features Ultralow power: as low as 23 μa in measurement mode and 0.1 μa in standby mode at = 2.5 V (typical) VS Power consumption scales automatically with bandwidth User-selectable resolution Fixed 10-bit resolution Full resolution, where resolution increases with g range, up to 13-bit resolution at ±16 g (maintaining 4 mg/lsb scale factor in all g ranges) Embedded memory management system with FIFO Single tap/double tap detection Activity/inactivity monitoring Free-fall detection 9

10 ADXL345 Digital Accelerometer Supply voltage range: 2.0 V to 3.6 V I/O voltage range: 1.7 V to V S SPI (3- and 4-wire) and I2C digital interfaces Flexible interrupt modes mappable to either interrupt pin Measurement ranges selectable via serial command Bandwidth selectable via serial command Wide temperature range ( 40 C to +85 C) 10,000 g shock survival Pb free/rohs compliant Small and thin: 3 mm 5 mm 1 mm LGA package 10

11 Functional Block Diagram 11

12 Pin Configuration 12

13 SPI Interface 3-wire and 4 wire mode (default) Mode 3: CPOL = 1, CPHA = 1 Clock frequency Data rate 3200Hz and 1600Hz: clock >= 2MHz Data rate 800Hz: clock >= 400KHz Remaining data rate scale proportionally (data rate x 500) 13

14 R/W Timing Diagram 14

15 Register Map 15

16 Register Map 16

17 Register Definition 17

18 Register Definition 18

19 Register Definition 19

20 Output Response 20

21 mbed Hardware Connection VS CS SDO INT1 INT2 ADXL345 VCC+5V GND SCL SDA/SDI +3.3V 21

22 Example x-axis 의가속도값을읽어서화면에출력 #include "mbed.h #define ADXL345_DEVID 0x00 #define ADXL345_POWER_CTR 0x2D #define ADXL345_DATA_FORMAT 0x31 #define ADXL345_DATA_X0 0x32 #define ADXL345_DATA_X1 0x33 #define ADXL345_DATA_Y0 0x34 #define ADXL345_DATA_Y1 0x35 #define ADXL345_DATA_Z0 0x36 #define ADXL345_DATA_Z1 0x37 #define POWER_MODE_MEASURE (0x01 << 3) #define FULL_RES (0x1 << 3) #define RANGE_2G 0 #define RANGE_4G 1 #define RANGE_8G 2 #define RANGE_16G 3 #define SPI_READ (0x1 << 7) #define SPI_WRITE (0x0 << 7) #define SPI_MB (0x1 << 6) 22

23 Example int8_t read_8(unsigned char address); void write_8(unsigned char address, unsigned char data); int16_t read_16(unsigned char address); void SPI_init(void); SPI SPI_port(p5, p6, p7); DigitalOut cs(p8); // mosi, miso, sclk // this acts as "Slave select int main() { unsigned char read_val; int accel_x; SPI_init(); read_val = read_8(adxl345_devid); // read device ID printf("device ID = %XH \n", read_val); write_8(adxl345_data_format, FULL_RES RANGE_16G); } while(1) { accel_x = read_16(adxl345_data_x0); printf("accel_x = %d \n", accel_x); wait(0.1); } 23

24 Example int8_t read_8(unsigned char address) { unsigned char received; cs = 0; SPI_port.write(address SPI_READ); received = SPI_port.write(0); cs = 1; wait_us(1); } return received; int16_t read_16(unsigned char address) { int16_t val; unsigned char *byte = (unsigned char *)&val; cs = 0; SPI_port.write(address SPI_READ SPI_MB); byte[0] = SPI_port.write(0); byte[1] = SPI_port.write(0); cs = 1; wait_us(1); } return val; 24

25 Example void write_8(unsigned char address, unsigned char data) { cs = 0; SPI_port.write(address SPI_WRITE); SPI_port.write(data); cs = 1; wait_us(1); } void SPI_init(void) { SPI_port.format(8,3); SPI_port.frequency(400000); wait(0.1); write_8(adxl345_power_ctr, POWER_MODE_MEASURE); // Measurement mode wait_us(10); } 25