MSP430 I²C 总线：时钟和数据之间的相位

Question

I am currently trying to use the TI MSP430 sample code to send commands from my MSP430FR2512 microcontroller to a PCA9955B LED driver. Unfortunately, I don't receive an acknowledgment from the driver (address is 0x01). It seems like clock and SDA are half a period shifted and not by 1/4 period as shown in a TI document :

TI I2C Timing Diagram

Measured I2C Communication

Is this normal?

This is the slightly changed example code I used (essentially only using the init and master write functions):

//******************************************************************************
//   MSP430FR2422 Demo - eUSCI_B0, I2C Master multiple byte TX/RX
//
//   Description: I2C master communicates to I2C slave sending and receiving
//   3 different messages of different length. I2C master will enter LPM0 mode
//   while waiting for the messages to be sent/receiving using I2C interrupt.
//   ACLK = NA, MCLK = SMCLK = DCO 16MHz.
//
//                                     /|\ /|\
//                   MSP430FR2422      4.7k |
//                 -----------------    |  4.7k
//            /|\ |             P1.3|---+---|-- I2C Clock (UCB0SCL)
//             |  |                 |       |
//             ---|RST          P1.2|-------+-- I2C Data (UCB0SDA)
//                |                 |
//                |                 |
//                |                 |
//                |                 |
//                |                 |
//                |                 |
//
//   Lixin Chen and Xiaodong Li
//   Texas Instruments Inc.
//   Dec 2020
//   Built with CCS V10.1
//******************************************************************************

#include <msp430.h> 
#include <stdint.h>
#include <stdbool.h>

//******************************************************************************
// Pin Config ******************************************************************
//******************************************************************************

#define LED_OUT     P1OUT
#define LED_DIR     P1DIR
#define LED0_PIN    BIT0
#define LED1_PIN    BIT1

//******************************************************************************
// Example Commands ************************************************************
//******************************************************************************

#define SLAVE_ADDR  0x01

/* CMD_TYPE_X_SLAVE are example commands the master sends to the slave.
 * The slave will send example SlaveTypeX buffers in response.
 *
 * CMD_TYPE_X_MASTER are example commands the master sends to the slave.
 * The slave will initialize itself to receive MasterTypeX example buffers.
 * */

#define CMD_TYPE_0_SLAVE      0
#define CMD_TYPE_1_SLAVE      1
#define CMD_TYPE_2_SLAVE      2

#define CMD_TYPE_2_MASTER      5

#define TYPE_0_LENGTH   1
#define TYPE_1_LENGTH   1
#define TYPE_2_LENGTH   1

#define MAX_BUFFER_SIZE     20

/* MasterTypeX are example buffers initialized in the master, they will be
 * sent by the master to the slave.
 * SlaveTypeX are example buffers initialized in the slave, they will be
 * sent by the slave to the master.
 * */

uint8_t Message1_Reg = 0x02;
uint8_t Message2_Reg = 0x45;

uint8_t Message1 [TYPE_2_LENGTH] = {0x14}; // LED 1,2 fully on
uint8_t Message2 [TYPE_2_LENGTH] = {0xFF}; // All LEDs full gain
//uint8_t MasterType2 [TYPE_2_LENGTH] = {'F', '4', '1', '9', '2', 'B'};
//uint8_t MasterType1 [TYPE_1_LENGTH] = { 8, 9};
//uint8_t MasterType0 [TYPE_0_LENGTH] = { 11};


uint8_t SlaveType2 [TYPE_2_LENGTH] = {0};
uint8_t SlaveType1 [TYPE_1_LENGTH] = {0};
uint8_t SlaveType0 [TYPE_0_LENGTH] = {0};

//******************************************************************************
// General I2C State Machine ***************************************************
//******************************************************************************

typedef enum I2C_ModeEnum{
    IDLE_MODE,
    NACK_MODE,
    TX_REG_ADDRESS_MODE,
    RX_REG_ADDRESS_MODE,
    TX_DATA_MODE,
    RX_DATA_MODE,
    SWITCH_TO_RX_MODE,
    SWITHC_TO_TX_MODE,
    TIMEOUT_MODE
} I2C_Mode;


/* Used to track the state of the software state machine*/
I2C_Mode MasterMode = IDLE_MODE;

/* The Register Address/Command to use*/
uint8_t TransmitRegAddr = 0;

/* ReceiveBuffer: Buffer used to receive data in the ISR
 * RXByteCtr: Number of bytes left to receive
 * ReceiveIndex: The index of the next byte to be received in ReceiveBuffer
 * TransmitBuffer: Buffer used to transmit data in the ISR
 * TXByteCtr: Number of bytes left to transfer
 * TransmitIndex: The index of the next byte to be transmitted in TransmitBuffer
 * */
uint8_t ReceiveBuffer[MAX_BUFFER_SIZE] = {0};
uint8_t RXByteCtr = 0;
uint8_t ReceiveIndex = 0;
uint8_t TransmitBuffer[MAX_BUFFER_SIZE] = {0};
uint8_t TXByteCtr = 0;
uint8_t TransmitIndex = 0;



/* I2C Write and Read Functions */

/* For slave device with dev_addr, writes the data specified in *reg_data
 *
 * dev_addr: The slave device address.
 *           Example: SLAVE_ADDR
 * reg_addr: The register or command to send to the slave.
 *           Example: CMD_TYPE_0_MASTER
 * *reg_data: The buffer to write
 *           Example: MasterType0
 * count: The length of *reg_data
 *           Example: TYPE_0_LENGTH
 *  */
I2C_Mode I2C_Master_WriteReg(uint8_t dev_addr, uint8_t reg_addr, uint8_t *reg_data, uint8_t count);

/* For slave device with dev_addr, read the data specified in slaves reg_addr.
 * The received data is available in ReceiveBuffer
 *
 * dev_addr: The slave device address.
 *           Example: SLAVE_ADDR
 * reg_addr: The register or command to send to the slave.
 *           Example: CMD_TYPE_0_SLAVE
 * count: The length of data to read
 *           Example: TYPE_0_LENGTH
 *  */
I2C_Mode I2C_Master_ReadReg(uint8_t dev_addr, uint8_t reg_addr, uint8_t count);
void CopyArray(uint8_t *source, uint8_t *dest, uint8_t count);

bool i2c_write_byte(uint8_t byte);


I2C_Mode I2C_Master_ReadReg(uint8_t dev_addr, uint8_t reg_addr, uint8_t count)
{
    /* Initialize state machine */
    MasterMode = TX_REG_ADDRESS_MODE;
    TransmitRegAddr = reg_addr;
    RXByteCtr = count;
    TXByteCtr = 0;
    ReceiveIndex = 0;
    TransmitIndex = 0;

    /* Initialize slave address and interrupts */
    UCB0I2CSA = dev_addr;
    UCB0IFG &= ~(UCTXIFG + UCRXIFG);       // Clear any pending interrupts
    UCB0IE &= ~UCRXIE;                       // Disable RX interrupt
    UCB0IE |= UCTXIE;                        // Enable TX interrupt

    UCB0CTLW0 |= UCTR + UCTXSTT;             // I2C TX, start condition
    __bis_SR_register(LPM0_bits + GIE);              // Enter LPM0 w/ interrupts

    return MasterMode;

}


I2C_Mode I2C_Master_WriteReg(uint8_t dev_addr, uint8_t reg_addr, uint8_t *reg_data, uint8_t count)
{
    /* Initialize state machine */
    MasterMode = TX_REG_ADDRESS_MODE;
    TransmitRegAddr = reg_addr;

    //Copy register data to TransmitBuffer
    CopyArray(reg_data, TransmitBuffer, count);

    TXByteCtr = count;
    RXByteCtr = 0;
    ReceiveIndex = 0;
    TransmitIndex = 0;

    /* Initialize slave address and interrupts */
    UCB0I2CSA = dev_addr;
    UCB0IFG &= ~(UCTXIFG + UCRXIFG);       // Clear any pending interrupts
    UCB0IE &= ~UCRXIE;                       // Disable RX interrupt
    UCB0IE |= UCTXIE;                        // Enable TX interrupt

    UCB0CTLW0 |= UCTR + UCTXSTT;             // I2C TX, start condition
    __bis_SR_register(LPM0_bits + GIE);              // Enter LPM0 w/ interrupts

    return MasterMode;
}



void CopyArray(uint8_t *source, uint8_t *dest, uint8_t count)
{
    uint8_t copyIndex = 0;
    for (copyIndex = 0; copyIndex < count; copyIndex++)
    {
        dest[copyIndex] = source[copyIndex];
    }
}


//******************************************************************************
// Device Initialization *******************************************************
//******************************************************************************


void initGPIO()
{
    // Configure GPIO
    //LED_OUT &= ~(LED0_PIN | LED1_PIN); // P1 setup for LED & reset output
    //LED_DIR |= (LED0_PIN | LED1_PIN);

    // I2C pins
    P1OUT  |= BIT2 | BIT3;
    //P1REN  |= BIT2 | BIT3;
    P1SEL0 |= BIT2 | BIT3;
    P1SEL1 &= ~(BIT2 | BIT3);

    // I2C Level Shifter Enable
    P1OUT &= ~BIT1;                         // Clear P1.1 output latch for a defined power-on state
    P1DIR |= BIT1;                          // Set P1.1 to output direction
    P1OUT |= BIT1;                          // Turn on P1.1

    // 5V DCDC Converter Enable
    P2OUT &= ~BIT2;                         // Clear P2.2 output latch for a defined power-on state
    P2DIR |= BIT2;                          // Set P2.2 to output direction
    P2OUT |= BIT2;                          // Turn on P2.2

    // Disable the GPIO power-on default high-impedance mode to activate
    // previously configured port settings
    PM5CTL0 &= ~LOCKLPM5;
}

void initClockTo16MHz()
{
    // Configure one FRAM waitstate as required by the device datasheet for MCLK
    // operation beyond 8MHz _before_ configuring the clock system.
    FRCTL0 = FRCTLPW | NWAITS_1;

    // Clock System Setup
    __bis_SR_register(SCG0);                           // disable FLL
    CSCTL3 |= SELREF__REFOCLK;                         // Set REFO as FLL reference source
    CSCTL0 = 0;                                        // clear DCO and MOD registers
    CSCTL1 &= ~(DCORSEL_7);                            // Clear DCO frequency select bits first
    CSCTL1 |= DCORSEL_5;                               // Set DCO = 16MHz
    CSCTL2 = FLLD_0 + 487;                             // DCOCLKDIV = 16MHz
    __delay_cycles(3);
    __bic_SR_register(SCG0);                           // enable FLL
    while(CSCTL7 & (FLLUNLOCK0 | FLLUNLOCK1));         // FLL locked
}

void initI2C()
{
    UCB0CTLW0 = UCSWRST;                      // Enable SW reset
    UCB0CTLW0 |= UCMODE_3 | UCMST | UCSSEL__SMCLK | UCSYNC; // I2C master mode, SMCLK
    UCB0BRW = 160;                            // fSCL = SMCLK/160 = ~100kHz
    UCB0I2CSA = SLAVE_ADDR;                   // Slave Address
    UCB0CTLW0 &= ~UCSWRST;                    // Clear SW reset, resume operation
    UCB0IE |= UCNACKIE;
}


//******************************************************************************
// Main ************************************************************************
// Send and receive three messages containing the example commands *************
//******************************************************************************

int main(void) {
    WDTCTL = WDTPW | WDTHOLD;   // Stop watchdog timer
    initClockTo16MHz();
    initGPIO();
    initI2C();

    //I2C_Master_WriteReg(SLAVE_ADDR, CMD_TYPE_0_MASTER, MasterType0, TYPE_0_LENGTH);
    //I2C_Master_WriteReg(SLAVE_ADDR, CMD_TYPE_1_MASTER, MasterType1, TYPE_1_LENGTH);

    I2C_Master_WriteReg(SLAVE_ADDR, Message1_Reg, Message1, TYPE_2_LENGTH);
    I2C_Master_WriteReg(SLAVE_ADDR, Message2_Reg, Message2, TYPE_2_LENGTH);

    /*

    I2C_Master_ReadReg(SLAVE_ADDR, CMD_TYPE_0_SLAVE, TYPE_0_LENGTH);
    CopyArray(ReceiveBuffer, SlaveType0, TYPE_0_LENGTH);

    I2C_Master_ReadReg(SLAVE_ADDR, CMD_TYPE_1_SLAVE, TYPE_1_LENGTH);
    CopyArray(ReceiveBuffer, SlaveType1, TYPE_1_LENGTH);

    I2C_Master_ReadReg(SLAVE_ADDR, CMD_TYPE_2_SLAVE, TYPE_2_LENGTH);
    CopyArray(ReceiveBuffer, SlaveType2, TYPE_2_LENGTH);

     */

    __bis_SR_register(LPM0_bits + GIE);



    return 0;
}


//******************************************************************************
// I2C Interrupt ***************************************************************
//******************************************************************************

#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector = USCI_B0_VECTOR
__interrupt void USCI_B0_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(USCI_B0_VECTOR))) USCI_B0_ISR (void)
#else
#error Compiler not supported!
#endif
{
  //Must read from UCB0RXBUF
  uint8_t rx_val = 0;
  switch(__even_in_range(UCB0IV, USCI_I2C_UCBIT9IFG))
  {
    case USCI_NONE:          break;         // Vector 0: No interrupts
    case USCI_I2C_UCALIFG:   break;         // Vector 2: ALIFG
    case USCI_I2C_UCNACKIFG:                // Vector 4: NACKIFG
      break;
    case USCI_I2C_UCSTTIFG:  break;         // Vector 6: STTIFG
    case USCI_I2C_UCSTPIFG:  break;         // Vector 8: STPIFG
    case USCI_I2C_UCRXIFG3:  break;         // Vector 10: RXIFG3
    case USCI_I2C_UCTXIFG3:  break;         // Vector 12: TXIFG3
    case USCI_I2C_UCRXIFG2:  break;         // Vector 14: RXIFG2
    case USCI_I2C_UCTXIFG2:  break;         // Vector 16: TXIFG2
    case USCI_I2C_UCRXIFG1:  break;         // Vector 18: RXIFG1
    case USCI_I2C_UCTXIFG1:  break;         // Vector 20: TXIFG1
    case USCI_I2C_UCRXIFG0:                 // Vector 22: RXIFG0
        rx_val = UCB0RXBUF;
        if (RXByteCtr)
        {
          ReceiveBuffer[ReceiveIndex++] = rx_val;
          RXByteCtr--;
        }

        if (RXByteCtr == 1)
        {
          UCB0CTLW0 |= UCTXSTP;
        }
        else if (RXByteCtr == 0)
        {
          UCB0IE &= ~UCRXIE;
          MasterMode = IDLE_MODE;
          __bic_SR_register_on_exit(CPUOFF);      // Exit LPM0
        }
        break;
    case USCI_I2C_UCTXIFG0:                 // Vector 24: TXIFG0
        switch (MasterMode)
        {
          case TX_REG_ADDRESS_MODE:
              UCB0TXBUF = TransmitRegAddr;
              if (RXByteCtr)
                  MasterMode = SWITCH_TO_RX_MODE;   // Need to start receiving now
              else
                  MasterMode = TX_DATA_MODE;        // Continue to transmision with the data in Transmit Buffer
              break;

          case SWITCH_TO_RX_MODE:
              UCB0IE |= UCRXIE;              // Enable RX interrupt
              UCB0IE &= ~UCTXIE;             // Disable TX interrupt
              UCB0CTLW0 &= ~UCTR;            // Switch to receiver
              MasterMode = RX_DATA_MODE;    // State state is to receive data
              UCB0CTLW0 |= UCTXSTT;          // Send repeated start
              if (RXByteCtr == 1)
              {
                  //Must send stop since this is the N-1 byte
                  while((UCB0CTLW0 & UCTXSTT));
                  UCB0CTLW0 |= UCTXSTP;      // Send stop condition
              }
              break;

          case TX_DATA_MODE:
              if (TXByteCtr)
              {
                  UCB0TXBUF = TransmitBuffer[TransmitIndex++];
                  TXByteCtr--;
              }
              else
              {
                  //Done with transmission
                  UCB0CTLW0 |= UCTXSTP;     // Send stop condition
                  MasterMode = IDLE_MODE;
                  UCB0IE &= ~UCTXIE;                       // disable TX interrupt
                  __bic_SR_register_on_exit(CPUOFF);      // Exit LPM0
              }
              break;

          default:
              __no_operation();
              break;
        }
        break;
    default: break;
  }
}

On the custom PCB I have a direct connection from the MSP430 via a TCA9406 I2C level shifter with integrated pull-ups to the PCA9955B. I measured on the side B of the level shifter.

Schematic Detail

Best, Josh

Answer 1

I found my stupid mistake. The PCA9955B requires an EXTERNAL pull-up resistor on its ~RESET pin.

PCA9955B Pin Description

I2C seems to be working fine.

Best, Josh