max30205 + nRF52 DK How to read more than 1 byte?

Question

I have established a connection with max30205, but I get only the first byte of temperature, how to read the second one? to get the tenths of a degree. 
 Now it works like: start / address / reading / stop 
 ret_code_t err_code1 = nrf_drv_twi_rx(&m_twi, max30205_ address , &m_sample, sizeof(m_sample)); APP_ERROR_CHECK(err_code1); while (m_xfer_done == false) 
 I necessary need : start / address / reading / reading / stop 
 What function should be used for this?

#include <stdio.h>
#include "boards.h"
#include "app_util_platform.h"
#include "app_error.h"
#include "nrf_drv_twi.h"
#include "nrf_delay.h"
//#include "nrf_twi_mngr.h"

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

/* TWI instance ID. */
#define TWI_INSTANCE_ID 0

/* Common addresses definition for temperature sensor. */
#define LM75B_ADDR (0x90U >> 1)

#define LM75B_REG_TEMP 0x00U
#define LM75B_REG_CONF 0x01U
#define LM75B_REG_THYST 0x02U
#define LM75B_REG_TOS 0x03U

/* Mode for LM75B. */
#define NORMAL_MODE 0U

/* Indicates if operation on TWI has ended. */
static volatile bool m_xfer_done = false;

/* TWI instance. */
static const nrf_drv_twi_t m_twi = NRF_DRV_TWI_INSTANCE(TWI_INSTANCE_ID);

/* Buffer for samples read from temperature sensor. */
static uint8_t m_sample;

/**
 * @brief Function for setting active mode on MMA7660 accelerometer.
 */
void LM75B_set_mode(void)
{
 ret_code_t err_code;

 /* Writing to LM75B_REG_CONF "0" set temperature sensor in NORMAL mode. */
 uint8_t reg[2] = {LM75B_REG_CONF, NORMAL_MODE};
 err_code = nrf_drv_twi_tx(&m_twi, LM75B_ADDR, reg, sizeof(reg), false);
 APP_ERROR_CHECK(err_code);
 while (m_xfer_done == false);

 /* Writing to pointer byte. */
 reg[0] = LM75B_REG_TEMP;
 m_xfer_done = false;
 err_code = nrf_drv_twi_tx(&m_twi, LM75B_ADDR, reg, 1, false);
 APP_ERROR_CHECK(err_code);
 while (m_xfer_done == false);
}

/**
 * @brief Function for handling data from temperature sensor.
 *
 * @param[in] temp Temperature in Celsius degrees read from sensor.
 */
__STATIC_INLINE void data_handler(uint8_t temp)
{
 NRF_LOG_INFO("Temperature: %d Celsius degrees.", temp);
}

/**
 * @brief TWI events handler.
 */
void twi_handler(nrf_drv_twi_evt_t const * p_event, void * p_context)
{
 switch (p_event->type)
 {
 case NRF_DRV_TWI_EVT_DONE:
 if (p_event->xfer_desc.type == NRF_DRV_TWI_XFER_RX)
 {
 data_handler(m_sample);
 }
 m_xfer_done = true;
 break;
 default:
 break;
 }
}

/**
 * @brief UART initialization.
 */
void twi_init (void)
{
 ret_code_t err_code;

 const nrf_drv_twi_config_t twi_lm75b_config = {
 .scl = ARDUINO_SCL_PIN,
 .sda = ARDUINO_SDA_PIN,
 .frequency = NRF_DRV_TWI_FREQ_100K,
 .interrupt_priority = APP_IRQ_PRIORITY_HIGH,
 .clear_bus_init = false
 };

 err_code = nrf_drv_twi_init(&m_twi, &twi_lm75b_config, twi_handler, NULL);
 APP_ERROR_CHECK(err_code);

 nrf_drv_twi_enable(&m_twi);
}

/**
 * @brief Function for reading data from temperature sensor.
 */
static void read_sensor_data()
{
 m_xfer_done = false;

 /* Read 1 byte from the specified address - skip 3 bits dedicated for fractional part of temperature. */
 ret_code_t err_code = nrf_drv_twi_rx(&m_twi, LM75B_ADDR, &m_sample, sizeof(m_sample));
 APP_ERROR_CHECK(err_code);
}

/**
 * @brief Function for main application entry.
 */
int main(void)
{

 APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
 NRF_LOG_DEFAULT_BACKENDS_INIT();

 NRF_LOG_INFO("
TWI sensor example started.");
 NRF_LOG_FLUSH();
 twi_init();
 LM75B_set_mode();
 ret_code_t err_code;
 while (true)
 {
 nrf_delay_ms(500);

 do
 {
 __WFE();
 }while (m_xfer_done == false);


 
 m_xfer_done = false;
 uint8_t reg[2] = {0x00U};
 err_code = nrf_drv_twi_tx(&m_twi, 0x48U, reg, sizeof(reg), true);
 APP_ERROR_CHECK(err_code);
 while (m_xfer_done == false);
 nrf_delay_ms(5);
 
 
 
 
 m_xfer_done = false;
 ret_code_t err_code1 = nrf_drv_twi_rx(&m_twi, 0x48U, &m_sample, sizeof(m_sample));
 APP_ERROR_CHECK(err_code1);
 while (m_xfer_done == false)

 NRF_LOG_FLUSH();
 
 }
}

/** @} */

Angus · Accepted Answer

Looks like the LM75 registers are arranged differently. 
 
 The max30502 returns a temperature value as a 16bit value ( 2 * byte reads ) which represents temperature in 0.00390625degC resolution. 
 Its a while since i played with this and can't remember the specifics of the nrf52 TWI driver but something along the lines of this below should get you started... 
 
 Made m_sample an array of length 2: 
 static uint8_t m_sample[2]; 
 
 In read_sensor_data(), the program will now read 2 bytes. 
 
 Wherever you deem appropriate ( perhaps in data_handler ) shift the 2 values into a uint16 by doing something similar to: 
 uint16_t tempVal = (m_sample[0] << 8) | m_sample[1]; 
 
 you can now get the value by multiplying by 0.00390625 
 float tempC = tempVal * (0.0390625);

I would also read the data sheet for the sensor. the configuration being written may be incorrect and may cause issues. In any case the default values are likely what you are wanting...

max30205 + nRF52 DK How to read more than 1 byte?

I have established a connection with max30205, but I get only the first byte of temperature, how to read the second one? to get the tenths of a degree.

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