MSP430F2471: MSP430F2471

Please provide the exact humidity sensor being used and keep in mind that some slave devices can respond to different slave addresses based on the logic level on dedicated pins.

Regards,
Ryan

Mr. Ryan the sensor is HYT271 humidity and temperature sensor. But I want to only read the humidity bytes. Here I am attaching the data sheet. 

My default address for the slave (0x28), write address(0x50) and read address (0x51). I have I have set I2CSA=0X28 (nominal address)    as per the example is given by TI there is no

clock and data seen. Then I have set it to write address (0x50) and the response is shown as below CRO screenshot. 

I have set I2CSA=0X50

(7bit address for 0x50 =1010000)

Is the configuration correct? and also

•   Why the 8bit is high (1) in CRO but it should be low (0)
•   Why there is no acknowledgment from the slave i.e 9th bit on SDA line should be low

How to get the acknowledgment. Please suggest the right configuration register for the slave write and read.

 

 

hyt-manual.pdf

Hi Swaroop,

UCB1I2CSA should be equal to 0x28 and UCTR should be reset for receiver mode, which results in a high read/write bit. The first eight bits should therefore be 01010001b, and if this is properly supplied then the HYT271 will acknowledge by pulling the data line low for the ninth clock. You should not generate the stop condition until you've actually received the necessary data bytes from the humidity sensor, please refer to the msp430x24x_uscib0_i2c_10.c example. Also note that the recommended pull-up resistances are 2.2 kOhm.

Regards,
Ryan

Dear Ryan, I have tried initially by setting I2CSA=0x28 (default slave address) but the humidity module but there are no traces observed on CRO.

And as you said, as per the code example I have changed my code
--------------------------------------------------------
#include <msp430.h>

unsigned char *PRxData; // Pointer to RX data
unsigned char RXByteCtr;
volatile unsigned char RxBuffer[128]; // Allocate 128 byte of RAM

int main(void)
{
WDTCTL = WDTPW + WDTHOLD; // Stop WDT
P5SEL |= 0x06; // Assign I2C pins to USCI_B0
UCB1CTL1 |= UCSWRST; // Enable SW reset
UCB1CTL0 = UCMST + UCMODE_3 + UCSYNC; // I2C Master, synchronous mode
UCB1CTL1 = UCSSEL_2 + UCSWRST; // Use SMCLK, keep SW reset
UCB1BR0 = 12; // fSCL = SMCLK/12 = ~100kHz
UCB1BR1 = 0;
UCB1I2CSA = 0x28; // Slave Address is 028h
UCB1CTL1 &= ~UCSWRST; // Clear SW reset, resume operation
UC1IE|= UCB0RXIE; // Enable RX interrupt

while (1)
{
PRxData = (unsigned char *)RxBuffer; // Start of RX buffer
RXByteCtr = 4; // Load RX byte counter
while (UCB1CTL1 & UCTXSTP); // Ensure stop condition got sent
UCB1CTL1 |= UCTXSTT; // I2C start condition
__bis_SR_register(CPUOFF + GIE); // Enter LPM0 w/ interrupts
// Remain in LPM0 until all data
// is RX'd
__no_operation(); // Set breakpoint >>here<< and
} // read out the RxBuffer buffer
}

//-------------------------------------------------------------------------------
// The USCI_B0 data ISR is used to move received data from the I2C slave
// to the MSP430 memory. It is structured such that it can be used to receive
// any 2+ number of bytes by pre-loading RXByteCtr with the byte count.
//-------------------------------------------------------------------------------
#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector = USCIAB1TX_VECTOR
__interrupt void USCIAB1TX_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(USCIAB1TX_VECTOR))) USCIAB1TX_ISR (void)
#else
#error Compiler not supported!
#endif
{
RXByteCtr--; // Decrement RX byte counter
if (RXByteCtr)
{
*PRxData++ = UCB1RXBUF; // Move RX data to address PRxData
if (RXByteCtr == 1) // Only one byte left?
UCB1CTL1 |= UCTXSTP; // Generate I2C stop condition
}
else
{
*PRxData = UCB1RXBUF; // Move final RX data to PRxData
__bic_SR_register_on_exit(CPUOFF); // Exit LPM0
}
}

My questions:
1. No traces observed with I2C1SA=0X28
2. Configuration to write the byte (0x50) to the sensor and read the byte from the sensor
3. How to use UCTR in the above code


Please help me out.


Regards,
Swaroop.

I don't know of a mechanism wherein the particular setting of I2CSA (in itself) causes the I2C unit to send/not send the address byte. I suspect there's something else going on.

What board are you using? (I don't recall a commodity board that uses the F2471.) Is the sensor the only (other) unit on the I2C bus? How are you triggering your scope?

Your previous program was probably a better test case. Did you try it with I2CSA=0x28?

Yes,  I have tried it with I2CSA=0X28 and the sensor is not giving any output on the oscilloscope.

I cannot suspect the sensor because I have got the reading by using the I/O lines(bit banging) and read the data from the sensor.

And the board is custom board designed by me and it is working with bit banging. I have used pull up resistances of 3.32K which is in the specified range.

I have triggered the scope of both SCL and SDA lines. The screenshot is already posted by me in the previous message on (Jan 3, 2018, 5:38 PM) with I2CSA=0X50 but not getting with I2CSA=0X28.

So, please suggest me the solution.

Thanks and Regards,

Swaroop.

One quick note, the code example provided uses UCB0RXIE instead of UCB1RXIE. They correspond to the same value so it actually will not affect your operation. Like Bruce, I have never heard of the USCI failing to send the slave addressed based on the contents of I2CSA. Does the start condition even get sent? Please provide a screenshot for reference. What happens if you disconnect the sensor from the bus and scope the MSP430 I2C output?

Regards,
Ryan