I have a project that has a MSP430G2553 master device and a Triple-Axis Digital-Output Gyro ITG-3200 Breakout slave. ITG3200 uses i²c protocol to communicate so i've been checking out the i²c module usage on Msp. For a starter i downloaded the TI I²c examples which can be found in http://www.ti.com/lsds/ti/microcontroller/16-bit_msp430/msp430_software_landing.page After i debugged the first code which is between a MSP master and a TMP100 temperature sensor as a slave. Here is the sample code.
//******************************************************************************
// MSP430G2xx3 Demo - USCI_B0 I2C Master to TMP100, Set P1.0 if Temp > 28C
//
// Description: I2C interface to TMP100 temperature sensor in 9-bit mode.
// Timer_A CCR0 interrupt is used to wake up and read the two bytes of
// the TMP100 temperature register every 62ms. If the temperature is greater
// than 28C, P1.0 is set, else reset. CPU is operated in LPM0. I2C speed
// is ~100kHz.
// ACLK = n/a, MCLK = SMCLK = TACLK = BRCLK = default DCO = ~1.2MHz
//
// /|\ /|\ /|\
// | TMP100 10k 10k MSP430G2xx3
// | ------- | | -------------------
// +--|Vcc SDA|<-|---+->|P1.7/UCB0SDA XIN|-
// | | | | | |
// +--|A1,A0 | | | XOUT|-
// | | | | |
// +--|Vss SCL|<-+------|P1.6/UCB0SCL P1.0|---> LED
// \|/ ------- | |
//
// D. Dang
// Texas Instruments Inc.
// February 2011
// Built with CCS Version 4.2.0 and IAR Embedded Workbench Version: 5.10
//******************************************************************************
#include <msp430.h>
unsigned int RxByteCtr;
unsigned int RxWord;
int main(void)
{
WDTCTL = WDTPW + WDTHOLD; // Stop WDT
P1DIR |= BIT0; // P1.0 output
P1SEL |= BIT6 + BIT7; // Assign I2C pins to USCI_B0
P1SEL2|= BIT6 + BIT7; // Assign I2C pins to USCI_B0
UCB0CTL1 |= UCSWRST; // Enable SW reset
UCB0CTL0 = UCMST + UCMODE_3 + UCSYNC; // I2C Master, synchronous mode
UCB0CTL1 = UCSSEL_2 + UCSWRST; // Use SMCLK, keep SW reset
UCB0BR0 = 12; // fSCL = SMCLK/12 = ~100kHz
UCB0BR1 = 0;
UCB0I2CSA = 0x4e; // Set slave address
UCB0CTL1 &= ~UCSWRST; // Clear SW reset, resume operation
IE2 |= UCB0RXIE; // Enable RX interrupt
TACTL = TASSEL_2 + MC_2; // SMCLK, contmode
while (1)
{
RxByteCtr = 2; // Load RX byte counter
UCB0CTL1 |= UCTXSTT; // I2C start condition
__bis_SR_register(CPUOFF + GIE); // Enter LPM0, enable interrupts
// Remain in LPM0 until all data
// is RX'd
if (RxWord < 0x1d00) // >28C?
P1OUT &= ~0x01; // No, P1.0 = 0
else
P1OUT |= 0x01; // Yes, P1.0 = 1
__disable_interrupt();
TACCTL0 |= CCIE; // TACCR0 interrupt enabled
__bis_SR_register(CPUOFF + GIE); // Enter LPM0, enable interrupts
// Remain in LPM0 until TACCR0
// interrupt occurs
TACCTL0 &= ~CCIE; // TACCR0 interrupt disabled
}
}
#pragma vector = TIMER0_A0_VECTOR
__interrupt void TA0_ISR(void)
{
__bic_SR_register_on_exit(CPUOFF); // Exit LPM0
}
// The USCIAB0TX_ISR is structured such that it can be used to receive any
// 2+ number of bytes by pre-loading RxByteCtr with the byte count.
#pragma vector = USCIAB0TX_VECTOR
__interrupt void USCIAB0TX_ISR(void)
{
RxByteCtr--; // Decrement RX byte counter
if (RxByteCtr)
{
RxWord = (unsigned int)UCB0RXBUF << 8; // Get received byte
if (RxByteCtr == 1) // Only one byte left?
UCB0CTL1 |= UCTXSTP; // Generate I2C stop condition
}
else
{
RxWord |= UCB0RXBUF; // Get final received byte,
// Combine MSB and LSB
__bic_SR_register_on_exit(CPUOFF); // Exit LPM0
}
}
I built up the same circuit where 2 10k pull ups on SDA and SCL, changed the slave address to either 0x69 or 0x68 which is the gyro address given in the user guide of the device. Since i did not built up any monitoring yet, i used an oscilloscope to check out the pulses on SCL and SDA. I didn't expect to see anything on SDA yet but what i am wondering is why i can't even see any clock cycle on SCL bus. It is either always on 3.3V (MSP internal vcc) or sometimes, its near 1V (0.80~). Even when i remove the gyroscope, SDA and SCL bus, i can't see any pulses on P1.6 port. Any ideas?
