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Problems getting an acknowledge from (any) slave, I2C Master Trasmit

Matthew Wasko
Intellectual 1670 points
Other Parts Discussed in Thread: MSP430F2013

Hi all,

I have been trying to send commands to a slave device using the MSP430F2013 as a master. However, I keep running into the problem of not getting an ACK after sending the slave device address onto the bus, which means that a STOP condition occurs instead of the data actually getting sent across the bus. I tried using two devices already, and I am already sure that my addressing is correct (looked at the datasheets, and made sure to shift up have LSB 0 for write, etc). I have heard that there may be subtle timing issues, that if I change my C code with regards to the timing of all of the conditions (START condition, sending slave address, one cycle for ACK/NACK, etc), it may just start working. This seems to be the only thing I can think of, as it seems like my project does not acknowledge any slave device (There is only one master and one slave on the bus). My C code is below:

// MSP430F20xx Demo - I2C Master Transmitter / Receiver, multiple bytes
//
// Description: I2C Master communicates with I2C Slave using
// the USI. Master data should increment from 0x55 with each transmitted byte
// and Master determines the number of bytes received, set by
// the Number_of_Bytes value. LED off for address or data Ack;
// LED on for address or data NAck.
// ACLK = n/a, MCLK = SMCLK = Calibrated 1MHz
//
//
// ***THIS IS THE MASTER CODE***
//
// Slave Master
// (msp430x20x3_usi_15.c)
// MSP430F20x2/3 MSP430F20x2/3
// ----------------- -----------------
// /|\| XIN|- /|\| XIN|-
// | | | | | |
// --|RST XOUT|- --|RST XOUT|-
// | | | |
// LED <-|P1.0 | | |
// | | | P1.0|-> LED
// | SDA/P1.7|------->|P1.6/SDA |
// | SCL/P1.6|<-------|P1.7/SCL |
//
// Note: internal pull-ups are used in this example for SDA & SCL
//
// R. B. Elliott / H. Grewal
// Texas Instruments Inc.
// February 2008
// Built with IAR Embedded Workbench Version: 3.42A
//******************************************************************************

#include <msp430.h>

#define number_of_bytes 2 // (slave address), register, data <-- YES, THIS SHOULD BE TWO
//#define number_of_bytes 5 // How many bytes?

void Master_Transmit(void);
void Master_Receive(void);

void Setup_USI_Master_TX(void);
void Setup_USI_Master_RX(void);

void read(char reg, char data);
void write(char reg, char data);

char reg_var;
char data_var;
unsigned int test;
char MST_Data = 0x06;
//char MST_Data = 0x55; // Variable for transmitted data
char SLV_Addr = 0xC0;
//char SLV_Addr = 0x90;
// MST_Data starts as 0x06 (register) and then changes to 0x1B (data)

int I2C_State, Bytecount, Transmit = 0; // State variable
void Data_TX (void);
void Data_RX (void);
int main(void)
{
volatile unsigned int i; // Use volatile to prevent removal

WDTCTL = WDTPW + WDTHOLD; // Stop watchdog
if (CALBC1_1MHZ==0xFF) // If calibration constants erased
{
while(1); // do not load, trap CPU!!
}
DCOCTL = 0; // Select lowest DCOx and MODx settings
BCSCTL1 = CALBC1_1MHZ; // Set DCO
DCOCTL = CALDCO_1MHZ;

P1OUT = 0xC0; // P1.6 & P1.7 Pullups, others to 0
P1REN |= 0xC0; // P1.6 & P1.7 Pullups
P1DIR = 0xFF; // Unused pins as outputs
P2OUT = 0;
P2DIR = 0xFF;

while(1)
{
Master_Transmit();
//_NOP(); // Used for IAR
//while(1);
//Master_Receive();
//_NOP();
}
}

/******************************************************
// USI interrupt service routine
// Data Transmit : state 0 -> 2 -> 4 -> 10 -> 12 -> 14
// Data Receive : state 0 -> 2 -> 4 -> 6 -> 8 -> 14
******************************************************/
#pragma vector = USI_VECTOR
__interrupt void USI_TXRX (void)
{
switch(__even_in_range(I2C_State,14))
{
case 0: // Generate Start Condition & send address to slave
//P1OUT |= 0x01; // LED on: sequence start
Bytecount = 0;
USISRL = 0x00; // Generate Start Condition...
USICTL0 |= USIGE+USIOE;
USICTL0 &= ~USIGE;
if (Transmit == 1){ // WRITE
USISRL = 0x90; // Address is 0x48 << 1 bit + 0 (rw)
}
if (Transmit == 0){ // READ
USISRL = 0x91; // 0x91 Address is 0x48 << 1 bit
// + 1 for Read
}
USICNT = (USICNT & 0xE0) + 0x08; // Bit counter = 8, TX Address
I2C_State = 2; // next state: rcv address (N)Ack
__delay_cycles(10);
break;
case 2: // Receive Address Ack/Nack bit
USICTL0 &= ~USIOE; // SDA = input
USICNT |= 0x01; // Bit counter=1, receive (N)Ack bit
I2C_State = 4; // Go to next state: check (N)Ack
break;
case 4: // Process Address Ack/Nack & handle data TX
if(Transmit == 1){ // WRITE00000000000000000000000000
USICTL0 |= USIOE; // SDA = output
if ((USISRL & 0x01)) // If Nack received... /////////////////////////////////////////////////////////////////////////////////////////////////////////
{ // Send stop...
USISRL = 0x00;
USICNT |= 0x01; // Bit counter=1, SCL high, SDA low
I2C_State = 14; // Go to next state: generate Stop
P1OUT |= 0x01; // Turn on LED: error
}
else
{ // Ack received, TX data to slave...
USISRL = MST_Data; // <-- MY SPECIAL CASE, FIRST SEND TO DEVICE SHOULD BE REGISTER (0x06)
//USISRL = MST_Data++; // Load data byte
USICNT |= 0x08; // Bit counter = 8, start TX
I2C_State = 10; // next state: receive data (N)Ack
Bytecount++;
//P1OUT &= ~0x01; // Turn off LED
break;
}
}
if(Transmit == 0){ // READ
if (USISRL & 0x01) // If Nack received
{ // Prep Stop Condition
USICTL0 |= USIOE;
USISRL = 0x00;
USICNT |= 0x01; // Bit counter= 1, SCL high, SDA low
I2C_State = 8; // Go to next state: generate Stop
P1OUT |= 0x01; // Turn on LED: error
}
else
{
Data_RX();
} // Ack received
}
break;
case 6: // Send Data Ack/Nack bit
USICTL0 |= USIOE; // SDA = output
if (Bytecount <= number_of_bytes-2)
{ // If this is not the last byte
USISRL = 0x00; // Send Ack
P1OUT &= ~0x01; // LED off
I2C_State = 4; // Go to next state: data/rcv again
Bytecount++;
}
else //last byte: send NACK
{
USISRL = 0xFF; // Send NAck
P1OUT |= 0x01; // LED on: end of comm
I2C_State = 8; // stop condition
}
USICNT |= 0x01; // Bit counter = 1, send (N)Ack bit
break;
case 8: // Prep Stop Condition
USICTL0 |= USIOE; // SDA = output
USISRL = 0x00;
USICNT |= 0x01; // Bit counter= 1, SCL high, SDA low
I2C_State = 14; // Go to next state: generate Stop
break;
case 10: // Receive Data Ack/Nack bit
USICTL0 &= ~USIOE; // SDA = input
USICNT |= 0x01; // Bit counter = 1, receive (N)Ack bit
I2C_State = 12; // Go to next state: check (N)Ack
break;
case 12: // Process Data Ack/Nack & send Stop
USICTL0 |= USIOE;
if (Bytecount == number_of_bytes){// If last byte
USISRL = 0x00;
I2C_State = 14; // Go to next state: generate Stop
P1OUT |= 0x01;
USICNT |= 0x01; } // set count=1 to trigger next state
else{
P1OUT &= ~0x01; // Turn off LED
Data_TX(); // TX byte
}
break;
case 14:// Generate Stop Condition
USISRL = 0x0FF; // USISRL = 1 to release SDA
USICTL0 |= USIGE; // Transparent latch enabled
USICTL0 &= ~(USIGE+USIOE); // Latch/SDA output disabled
I2C_State = 0; // Reset state machine for next xmt
LPM0_EXIT; // Exit active for next transfer
break;
}
USICTL1 &= ~USIIFG; // Clear pending flag
}

void Data_TX (void){
USISRL = 0x1B; // <-- MY SPECIAL CASE, I'M ASSUMING THAT AFTER SENDING REGISTER BYTE (0x06), I NOW HAVE TO SEND DATA BYTE (0x1B)
//USISRL = MST_Data++; // Load data byte
USICNT |= 0x08; // Bit counter = 8, start TX
I2C_State = 10; // next state: receive data (N)Ack
Bytecount++;
}

void Data_RX (void){
USICTL0 &= ~USIOE; // SDA = input --> redundant
USICNT |= 0x08; // Bit counter = 8, RX data
I2C_State = 6; // Next state: Test data and (N)Ack
P1OUT &= ~0x01; // LED off
}


void Setup_USI_Master_TX (void)
{
_DINT();
Bytecount = 0;
Transmit = 1;
USICTL0 = USIPE6+USIPE7+USIMST+USISWRST; // Port & USI mode setup
USICTL1 = USII2C+USIIE; // Enable I2C mode & USI interrupt
USICKCTL = USIDIV_7+USISSEL_2+USICKPL;
//USICKCTL = USIDIV_0+USISSEL_2+USICKPL; // USI clk: SCL = SMCLK/128
USICNT |= USIIFGCC; // Disable automatic clear control
USICTL0 &= ~USISWRST; // Enable USI
USICTL1 &= ~USIIFG; // Clear pending flag
_EINT();
}

void Setup_USI_Master_RX (void)
{
_DINT();
Bytecount = 0;
Transmit = 0;
USICTL0 = USIPE6+USIPE7+USIMST+USISWRST; // Port & USI mode setup
USICTL1 = USII2C+USIIE; // Enable I2C mode & USI interrupt
USICKCTL = USIDIV_7+USISSEL_2+USICKPL; // USI clks: SCL = SMCLK/128
USICNT |= USIIFGCC; // Disable automatic clear control
USICTL0 &= ~USISWRST; // Enable USI
USICTL1 &= ~USIIFG; // Clear pending flag
_EINT();
}

void Master_Transmit(void){
volatile unsigned int i;
Setup_USI_Master_TX();
USICTL1 |= USIIFG; // Set flag and start communication
LPM0; // CPU off, await USI interrupt
for (i = 0; i < 5000; i++); // Delay between comm cycles
}

void Master_Receive(void){
volatile unsigned int i;
Setup_USI_Master_RX();
USICTL1 |= USIIFG; // Set flag and start communication
LPM0; // CPU off, await USI interrupt
for (i = 0; i < 5000; i++); // Delay between comm cycles
}

void read(char reg, char data)
{
reg_var = reg;
data_var = data;
Master_Transmit();
}

void write(char reg, char data)
{
reg_var = reg;
data_var = data;
Master_Receive();
}

Any help would be greatly appreciated.

Matt

  • 0
    Genius 3370 points

    In the code you have this constant defined:

    char SLV_Addr = 0xC0;

    But in the ISR, the slave address is still hard coded.

    if (Transmit == 1){ // WRITE
    USISRL = 0x90; // Address is 0x48 << 1 bit + 0 (rw)
    }
    if (Transmit == 0){ // READ
    USISRL = 0x91; // 0x91 Address is 0x48 << 1 bit
    // + 1 for Read
    }

    Change the above code to this for starters:

     if (Transmit == 1){ // WRITE
    USISRL = SLV_Addr <<1; // Address is SLV_Addr << 1 bit + 0 (rw)
    }
    if (Transmit == 0){ // READ
    USISRL = SLV_Addr <<1 +1; // Address is SLV_ADDR << 1 bit
    // + 1 for Read
    }

    But for a better generic I2C master interface for the MSP430F2013 try this library:

    http://www.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=slaa368a

     

  • 0 in reply to Timothy Barr
    TI__Intellectual 1670 points

    Sorry, I was being lazy and just hard coding the addresses in correctly. That isn't the issue.

    Could it be that my slave device isn't recognizing the start condition and therefore isn't going to check to see if the next byte corresponds to its address? It's all very confusing for me, because I have run it on a GUI that actually works, and the waveforms look pretty similar to mine, so it would seem like my MSP430 should also create a proper ACK from the slave device, but its not.

    Matt

  • 0 in reply to Matthew Wasko
    TI__Intellectual 1670 points

    Update:

    I am currently trying to just make sure the waveforms for both the GUI (solution) and my MCU are matching. Apparently, they aren't matching enough as you can see below:

    The "a cursor" overlaps with the ninth clock cycle which checks for acknowledge, and in the second case, it stays high, which leads to a STOP condition. Two other noticeable differences are the fact that the START condition for the solution has SCL go low immediately after SDA goes low, as well as the fact that for the solution, the first clock cycle is about twice as long as the other clock cycles and SDA doesn't immediately go high (unlike the second case in which SDA goes high as soon as the first clock cycle starts low). Are these significant problems that are causing my slave device to NACK? I am currently trying to match these two waveforms, and I was provided with two defines:

    #define FORCING_SDA_HIGH() \
    { \
    USISRL = 0xFF; \
    USICTL0 |= USIGE; \
    USICTL0 &= ~(USIGE+USIOE); \
    }

    #define FORCING_SDA_LOW() \
    { \
    USISRL = 0x00; \
    USICTL0 |= USIGE+USIOE; \
    USICTL0 &= ~USIGE; \
    }

    If someone could help me make two defines for FORCING_SCL_HIGH/LOW, that would be really helpful as I try to match the waveforms as well as possible.

    Thanks,

    Matt

  • 0 in reply to Matthew Wasko
    Guru 227245 points

    While the second looks way better, regardign timing, there is a difference in the voltage levels. The first screenshot shows the low voltage as ~0V while the second only reaces ~0.4V. Which might be too high for the slave to be seen as a low transition. Especially if the slave has a rather low supply voltage.
    You should use a weaker pulldown. In theory, the MSP shoudl be able to get the voltage down to 0V, but only if it hasn't to drive much current. (see datasheet for details)

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