I am having a really tough time trying to get the I2C to work in the 2272. I meed to use a repeat start but I cant seem to get it to work. Can someone provide some tips on how to send this: S->Slave Address->W->ACL->Data->ACK->S->Slave Address->R->ACK->Data Byte Low->ACK->Data Byte High->ACK->PEC->ACK->STOP
1. Send START bit
2. Send Slave Address (0x00* for example) + Rd\-Wr bit**
3. Send Command (0b000x_xxxx + 0b0000_0111 -> 0b0000_0111)
4. Send Repeated START_bit
5. Send Slave Address + Rd\-Wr bit**
6. Read Data Byte Low (master must send ACK bit)
7. Read Data Byte High (master must send ACK bit)
8. Read PEC (master can send ACK or NACK)
9. Send STOP bit
I have looked at msp430x22x4_uscib0_i2c_12.c USCI_B0 I2C Master TX/RX multiple bytes from MSP430 Slave with a repeated start
but I dont really understand what is happening. The code for it is:
#include "msp430x22x4.h"
#define NUM_BYTES_TX 3 // How many bytes?
#define NUM_BYTES_RX 2
int RXByteCtr, RPT_Flag = 0; // enables repeated start when 1
volatile unsigned char RxBuffer[128]; // Allocate 128 byte of RAM
unsigned char *PTxData; // Pointer to TX data
unsigned char *PRxData; // Pointer to RX data
unsigned char TXByteCtr, RX = 0;
unsigned char MSData = 0x55;
void Setup_TX(void);
void Setup_RX(void);
void Transmit(void);
void Receive(void);
void main(void)
{
WDTCTL = WDTPW + WDTHOLD; // Stop WDT
P3SEL |= 0x06; // Assign I2C pins to USCI_B0
while(1){
//Transmit process
Setup_TX();
RPT_Flag = 1;
Transmit();
while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent
//Receive process
Setup_RX();
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
// any 2+ number of bytes by pre-loading RXByteCtr with the byte count.
//-------------------------------------------------------------------------------
#pragma vector = USCIAB0TX_VECTOR
__interrupt void USCIAB0TX_ISR(void)
{
if(RX == 1){ // Master Recieve?
RXByteCtr--; // Decrement RX byte counter
if (RXByteCtr)
{
*PRxData++ = UCB0RXBUF; // Move RX data to address PRxData
}
else
{
if(RPT_Flag == 0)
UCB0CTL1 |= UCTXSTP; // No Repeated Start: stop condition
if(RPT_Flag == 1){ // if Repeated Start: do nothing
RPT_Flag = 0;
}
*PRxData = UCB0RXBUF; // Move final RX data to PRxData
__bic_SR_register_on_exit(CPUOFF); // Exit LPM0
}}
else{ // Master Transmit
if (TXByteCtr) // Check TX byte counter
{
UCB0TXBUF = MSData++; // Load TX buffer
TXByteCtr--; // Decrement TX byte counter
}
else
{
if(RPT_Flag == 1){
RPT_Flag = 0;
PTxData = &MSData; // TX array start address
TXByteCtr = NUM_BYTES_TX; // Load TX byte counter
__bic_SR_register_on_exit(CPUOFF);
}
else{
UCB0CTL1 |= UCTXSTP; // I2C stop condition
IFG2 &= ~UCB0TXIFG; // Clear USCI_B0 TX int flag
__bic_SR_register_on_exit(CPUOFF); // Exit LPM0
}
}
}
}
void Setup_TX(void){
_DINT();
RX = 0;
IE2 &= ~UCB0RXIE;
while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent// Disable RX interrupt
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 = 0x48; // Slave Address is 048h
UCB0CTL1 &= ~UCSWRST; // Clear SW reset, resume operation
IE2 |= UCB0TXIE; // Enable TX interrupt
}
void Setup_RX(void){
_DINT();
RX = 1;
IE2 &= ~UCB0TXIE;
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 = 0x48; // Slave Address is 048h
UCB0CTL1 &= ~UCSWRST; // Clear SW reset, resume operation
IE2 |= UCB0RXIE; // Enable RX interrupt
}
void Transmit(void){
PTxData = &MSData; // TX array start address
TXByteCtr = NUM_BYTES_TX; // 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
}
void Receive(void){
PRxData = (unsigned char *)RxBuffer; // Start of RX buffer
RXByteCtr = NUM_BYTES_RX-1; // Load RX byte counter
while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent
UCB0CTL1 |= UCTXSTT; // I2C start condition
__bis_SR_register(CPUOFF + GIE); // Enter LPM0 w/ interrupts
}
