I've been trying to use an I²C bus between a MSP430G2553 launchpad and ITG-3200 gyroscope breakout. Here is the Launchpad datasheet and user guide and the ITG-3200 datasheet. The ITG-3200 uses a repeated start to read from a specific register. But not necessarily. After checking the example code on the Arduino (I checked the data flow on buses with an oscilloscope) I realised that even with a Stop-Start condition it should work. What I'm trying to do is to accomplish this on the MSP Launchpad.
I'm using two I²C examples provided from TI msp430g2xx3_uscib0_i2c_04 (single read) and msp430g2xx3_uscib0_i2c_06 (single write). I combined these two sets of code and came up with code for my ITG-3200 which uses a write operation followed by a read for reading it's registers. Here is the code:
#include <msp430.h>
int TXByteCtr = 1;
unsigned char PRxData; // Pointer to RX data
int Rx = 0;
unsigned char WHO_AM_I = 0x00;
void init_I2C(void);
void Transmit(void);
void Receive(void);
int main(void)
{
WDTCTL = WDTPW + WDTHOLD; // Stop WDT
P1SEL |= BIT6 + BIT7; // Assign I2C pins to USCI_B0
P1SEL2|= BIT6 + BIT7; // Assign I2C pins to USCI_B0
init_I2C();
while(1){
//Transmit process
Rx = 0;
Transmit();
while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent
//Receive process
Rx = 1;
Receive();
while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent
}
}
//-------------------------------------------------------------------------------
// 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
//-------------------------------------------------------------------------------
#pragma vector = USCIAB0TX_VECTOR
__interrupt void USCIAB0TX_ISR(void)
{
if(Rx == 1){ // Master Recieve?
PRxData = UCB0RXBUF; // Get RX data
__bic_SR_register_on_exit(CPUOFF); // Exit LPM0
}
else{ // Master Transmit
if (TXByteCtr) // Check TX byte counter
{
UCB0TXBUF = WHO_AM_I; // Load TX buffer
TXByteCtr--; // Decrement TX byte counter
}
else
{
UCB0CTL1 |= UCTXSTP; // I2C stop condition
IFG2 &= ~UCB0TXIFG; // Clear USCI_B0 TX int flag
__bic_SR_register_on_exit(CPUOFF); // Exit LPM0
}
}
}
void init_I2C(void) {
_DINT();
IE2 |= UCB0RXI //Enable RX interrupt
IE2 |= UCB0TXIE; // Enable TX interrupt
while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent
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 = 0x69; // Slave Address is 069h
UCB0CTL1 &= ~UCSWRST; // Clear SW reset, resume operation
}
void Transmit(void){
while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent
UCB0CTL1 |= UCTR + UCTXSTT; // I2C TX, start condition
__bis_SR_register(CPUOFF + GIE); // Enter LPM0 w/ interrupts
}
void Receive(void){
UCB0CTL1 &= ~UCTR ; // Clear UCTR
while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent
UCB0CTL1 |= UCTXSTT; // I2C start condition
while (UCB0CTL1 & UCTXSTT); // Start condition sent?
UCB0CTL1 |= UCTXSTP; // I2C stop condition
__bis_SR_register(CPUOFF + GIE); // Enter LPM0 w/ interrupts
}
I don't really know why is this happening but SDA and SCL clocks keeps locking to 0V. I'm sure about the circuit (full with pull-up resistors) because that is working on an Arduino. Can you point out what seems to be the problem here?
Edit: It is better if i put the two examples from TI resource here aswell.
It is better if i give the two example of TI here. Here is the master RX single byte from the slave: ( msp430g2xx3_uscib0_i2c_04.c )
/* --COPYRIGHT--,BSD_EX
* Copyright (c) 2012, Texas Instruments Incorporated
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* * Neither the name of Texas Instruments Incorporated nor the names of
* its contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*******************************************************************************
*
* MSP430 CODE EXAMPLE DISCLAIMER
*
* MSP430 code examples are self-contained low-level programs that typically
* demonstrate a single peripheral function or device feature in a highly
* concise manner. For this the code may rely on the device's power-on default
* register values and settings such as the clock configuration and care must
* be taken when combining code from several examples to avoid potential side
* effects. Also see www.ti.com/grace for a GUI- and www.ti.com/msp430ware
* for an API functional library-approach to peripheral configuration.
*
* --/COPYRIGHT--*/
//******************************************************************************
// MSP430G2xx3 Demo - USCI_B0 I2C Master RX single bytes from MSP430 Slave
//
// Description: This demo connects two MSP430's via the I2C bus. The master
// reads from the slave. This is the master code. The data from the slave
// transmitter begins at 0 and increments with each transfer. The received
// data is in R5 and is checked for validity. If the received data is
// incorrect, the CPU is trapped and the P1.0 LED will stay on. The USCI_B0
// RX interrupt is used to know when new data has been received.
// ACLK = n/a, MCLK = SMCLK = BRCLK = default DCO = ~1.2MHz
//
// /|\ /|\
// MSP430G2xx3 10k 10k MSP430G2xx3
// slave | | master
// ----------------- | | -----------------
// -|XIN P1.7/UCB0SDA|<-|---+->|P1.7/UCB0SDA XIN|-
// | | | | | 32kHz
// -|XOUT | | | XOUT|-
// | P1.6/UCB0SCL|<-+----->|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 char RXData;
unsigned char RXCompare;
int main(void)
{
WDTCTL = WDTPW + WDTHOLD; // Stop WDT
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 = 0x069; // Slave Address is 048h
UCB0CTL1 &= ~UCSWRST; // Clear SW reset, resume operation
IE2 |= UCB0RXIE; // Enable RX interrupt
RXCompare = 0; // Used to check incoming data
while (1)
{
while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent
UCB0CTL1 |= UCTXSTT; // I2C start condition
while (UCB0CTL1 & UCTXSTT); // Start condition sent?
UCB0CTL1 |= UCTXSTP; // I2C stop condition
__bis_SR_register(CPUOFF + GIE); // Enter LPM0 w/ interrupts
}
}
// USCI_B0 Data ISR
#pragma vector = USCIAB0TX_VECTOR
__interrupt void USCIAB0TX_ISR(void)
{
RXData = UCB0RXBUF; // Get RX data
__bic_SR_register_on_exit(CPUOFF); // Exit LPM0
}
And here is the Master TX single byte to the slave ( msp430g2xx3_uscib0_i2c_04.c )
/* --COPYRIGHT--,BSD_EX
* Copyright (c) 2012, Texas Instruments Incorporated
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* * Neither the name of Texas Instruments Incorporated nor the names of
* its contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*******************************************************************************
*
* MSP430 CODE EXAMPLE DISCLAIMER
*
* MSP430 code examples are self-contained low-level programs that typically
* demonstrate a single peripheral function or device feature in a highly
* concise manner. For this the code may rely on the device's power-on default
* register values and settings such as the clock configuration and care must
* be taken when combining code from several examples to avoid potential side
* effects. Also see www.ti.com/grace for a GUI- and www.ti.com/msp430ware
* for an API functional library-approach to peripheral configuration.
*
* --/COPYRIGHT--*/
//******************************************************************************
// MSP430G2xx3 Demo - USCI_B0 I2C Master TX single bytes to MSP430 Slave
//
// Description: This demo connects two MSP430's via the I2C bus. The master
// transmits to the slave. This is the master code. It continuously
// transmits 00h, 01h, ..., 0ffh and demonstrates how to implement an I2C
// master transmitter sending a single byte using the USCI_B0 TX interrupt.
// ACLK = n/a, MCLK = SMCLK = BRCLK = default DCO = ~1.2MHz
//
// /|\ /|\
// MSP430G2xx3 10k 10k MSP430G2xx3
// slave | | master
// ----------------- | | -----------------
// -|XIN P1.7/UCB0SDA|<-|---+->|P1.7/UCB0SDA XIN|-
// | | | | |
// -|XOUT | | | XOUT|-
// | P1.6/UCB0SCL|<-+----->|P1.6/UCB0SCL |
// | | | |
//
// 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 char TXData;
unsigned char TXByteCtr;
int main(void)
{
WDTCTL = WDTPW + WDTHOLD; // Stop WDT
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 = 0x69; // Slave Address is 048h
UCB0CTL1 &= ~UCSWRST; // Clear SW reset, resume operation
IE2 |= UCB0TXIE; // Enable TX interrupt
TXData = 0x00; // Holds TX data
while (1)
{
TXByteCtr = 1; // Load TX byte counter
while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent
UCB0CTL1 |= UCTR + UCTXSTT; // I2C TX, start condition
__bis_SR_register(CPUOFF + GIE); // Enter LPM0 w/ interrupts
// Remain in LPM0 until all data
// is TX'd
TXData++; // Increment data byte
}
}
//------------------------------------------------------------------------------
// The USCIAB0TX_ISR is structured such that it can be used to transmit any
// number of bytes by pre-loading TXByteCtr with the byte count.
//------------------------------------------------------------------------------
#pragma vector = USCIAB0TX_VECTOR
__interrupt void USCIAB0TX_ISR(void)
{
if (TXByteCtr) // Check TX byte counter
{
UCB0TXBUF = TXData; // Load TX buffer
TXByteCtr--; // Decrement TX byte counter
}
else
{
UCB0CTL1 |= UCTXSTP; // I2C stop condition
IFG2 &= ~UCB0TXIFG; // Clear USCI_B0 TX int flag
__bic_SR_register_on_exit(CPUOFF); // Exit LPM0
}
}
Best Answer
Here is the code that reading a single byte via I²C. Do not forget to connect 2 pull-up resistors on P1.6 and P1.7. These are the SDA and SCL lines on I2C bus.