Hi, I am working with Humidity sensor HYT271. It is working fine with bit banging using I2C(I have used I/O lines of MSP430) using external pull-ups. But, to work efficiently I want to use internal i2c. The IDE is code composer studio. The code examples are given for i2c but I am confused to start with that.
Can anyone help me out how to use internal i2c exactly? and provide sample code for any sensor.
The state of SDA and SCL is high with power on due to external 3.3K pull-ups. So, What's wrong with IE.
Can you suggest the right configuration for it?
First thing I want to do is generate the clock, and start condition and wait for the sensor acknowledgment.
Afterwards, I will think about reading the sensor data.
I had finally got SCL and SDA output from the sensor by going through the datasheet and application report. But still, I have some issues.
Things I have done to generate clock and data:
***************************************************
UCB1BR0 = 12; // fSCL =SMCLK/12 = ~100kHz
UCB1BR1 = 0;
UCB1I2CSA = 0x51; // default slave address (0x28 )given in the sensor data sheet
*******Continuous loop for Start,and Stop and Write address of Slave *****************
while(1)
{
UCB1CTL1 |= UCTXSTT; // I2C start condition
UCB1CTL1 |= UCTXSTP; // Generate I2C stop condition
}
Other than above I have set necessary configurations for USCI module.
My question as per I2C protocol and data sheet gave the Start sequence, 7-bit slave address, and write bit the calculated byte for the slave write address 0x28 are 0x51.
So I have set UCB1I2CSA = 0x51.
So, after transmitting start, slave write address the acknowledgment has to be given from the sensor in the 9th clock pulse by making the SDA line low which is not happening.
The clock pulses generated are like spikes. Are they correct? Is there anything required for the clock pulses.
Can anyone help me to analyze this situation? I have seen this response from the CRO.
Hi to all,
From the above solutions suggested I have tried with I got something by putting I2C1SA=0X28 with the following code. Let's have a look.
The below code is working when these 2 lines are commented.
change 1.
//__bis_SR_register(CPUOFF + GIE);
change 2.
// __bic_SR_register_on_exit(CPUOFF); // Exit LPM0
I don't know why there are no traces of SCL and SDA when I uncomment above 2 lines.
I have used this line of code to enable Interrupts.
Change 3.
__bis_SR_register(GIE);
Change 4:
RXByteCtr=2
The below is the screenshot on the oscilloscope for the following code.
//********************************************************************//
#include "msp430x24x.h"
#include "stdio.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
BCSCTL1 &= ~XT2OFF; // Activate XT2 high freq xtal
BCSCTL2 =0x88;
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 0x28
UCB1CTL1 &= ~UCSWRST; // Clear SW reset, resume operation
UC1IE |= UCB1RXIE; // Enable RX interrupt
__bis_SR_register(GIE);
while (1)
{
PRxData = (unsigned char *)RxBuffer; // Start of RX buffer
RXByteCtr = 2; // 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. What is the value to be loaded into RXByteCtr, How to choose the value and Is my value 2 is correct?
2. For the above code am I getting the 2 bytes humidity data from the sensor? If not how to read using UCTR bit suggest the code sample for reading using UCTR
3. How to see the UCB1RXBUF data in debug mode I am not able to see any value in the register when I set the breakpoint. I have not mentioned any uart code in above code.
But I have sent UCB1RXBUF using the uart on to hyper terminal, hex values observed are some 00 and 8.
Help me to solve this.
Regards,
Swaroop.
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