CCS: BQ76940 I2C communication, register reading issue

Tool/software: Code Composer Studio

hi

i am using an BQ76940EVM product working with DSP f28335 through I2C communcation. for purpose of using 12 cells, i already short circuit input pin 3-4, 8-9, 13-14. sometime they work well together for a few minutes, and after that suddenly stop working, i recognize that the DSP are unable to read the BQ76940's registers. please give me solution. i'll also post my code here. thank you.

void Update_Cell_Voltage_Current(void)
{

Uint16 i=0, k=4;
//Read voltage of cell 1
// Send START and set pointer to VC1_HI - register
I2caRegs.I2CCNT = 1; // 1 byte message,
I2caRegs.I2CDXR = VC1_HI; // target here: pointer to VC1_HI register
// Send start as master transmitter
I2caRegs.I2CMDR.all = 0x6620; // transmitter mode
/* Bit15 = 0; no NACK in receiver mode
Bit14 = 1; FREE on emulation halt
Bit13 = 1; STT generate START
Bit12 = 0; reserved
Bit11 = 0; STP not generate STOP
Bit10 = 1; MST master mode
Bit9 = 1; TRX master - transmitter mode
Bit8 = 0; XA 7 bit address mode
Bit7 = 0; RM nonrepeat mode, I2CCNT determines # of bytes
Bit6 = 0; DLB no loopback mode
Bit5 = 1; IRS I2C module enabled
Bit4 = 0; STB no start byte mode
Bit3 = 0; FDF no free data format
Bit2-0: 0; BC 8 bit per data byte */
while(I2caRegs.I2CSTR.bit.ARDY == 0); // wait for access ready condition

I2caRegs.I2CCNT = 1; // read 1 byte
I2caRegs.I2CMDR.all = 0x6C20; //receiver mode
/* Bit15 = 0; no NACK in receiver mode
Bit14 = 1; FREE on emulation halt
Bit13 = 1; STT generate START
Bit12 = 0; reserved
Bit11 = 1; STP generate STOP
Bit10 = 1; MST master mode
Bit9 = 0; TRX master - receiver mode
Bit8 = 0; XA 7 bit address mode
Bit7 = 0; RM nonrepeat mode, I2CCNT determines # of bytes
Bit6 = 0; DLB no loopback mode
Bit5 = 1; IRS I2C module enabled
Bit4 = 0; STB no start byte mode
Bit3 = 0; FDF no free data format
Bit2-0: 0; BC 8 bit per data byte */

// while(I2caRegs.I2CSTR.bit.RRDY == 0); // wait for 1st byte

Voltage_regs[0] = I2caRegs.I2CDRR << 8; // read upper 8 Bit (integers)
// RRDY is automatically cleared by read of I2CDRR

// Send START and set pointer to VC1_LO - register
I2caRegs.I2CCNT = 1; // 1 byte message,
I2caRegs.I2CDXR = VC1_LO; // target here: pointer to VC1_LO register
// Send start as master transmitter
I2caRegs.I2CMDR.all = 0x6620; // transmitter mode
while(I2caRegs.I2CSTR.bit.ARDY == 0); // wait for access ready condition

I2caRegs.I2CCNT = 1; // read 1 byte
I2caRegs.I2CMDR.all = 0x6C20; // receiver mode

// while(I2caRegs.I2CSTR.bit.RRDY == 0); // wait for 2nd byte

Voltage_regs[0] += I2caRegs.I2CDRR; // read lower 8 Bit (integers)

//Read voltage of cell 2
// Send START and set pointer to VC2_HI - register
I2caRegs.I2CCNT = 1; // 1 byte message,
I2caRegs.I2CDXR = VC2_HI; // target here: pointer to VC2_HI register
// Send start as master transmitter
I2caRegs.I2CMDR.all = 0x6620; // transmitter mode
while(I2caRegs.I2CSTR.bit.ARDY == 0); // wait for access ready condition

// Read 1st byte
I2caRegs.I2CCNT = 1; // read 1 byte
I2caRegs.I2CMDR.all = 0x6C20; //receiver mode
// while(I2caRegs.I2CSTR.bit.RRDY == 0); // wait for 1st byte

Voltage_regs[1] = I2caRegs.I2CDRR << 8; // read upper 8 Bit (integers)
// RRDY is automatically cleared by read of I2CDRR
// Send START and set pointer to VC2_LO - register
I2caRegs.I2CCNT = 1; // 1 byte message,
I2caRegs.I2CDXR = VC2_LO; // target here: pointer to VC2_HI register
// Send start as master transmitter
I2caRegs.I2CMDR.all = 0x6620; // transmitter mode

while(I2caRegs.I2CSTR.bit.ARDY == 0); // wait for access ready condition
// Read 2sd byte
I2caRegs.I2CCNT = 1; // read 1 byte
I2caRegs.I2CMDR.all = 0x6C20; // receiver mode
// while(I2caRegs.I2CSTR.bit.RRDY == 0); // wait for 2nd byte

Voltage_regs[1] += I2caRegs.I2CDRR; // read lower 8 Bit (fractions)

//Read voltage of cell 3 (cell 3 in the battery string is cell 5 of the monitoring IC)
// Send START and set pointer to VC6_HI - register
I2caRegs.I2CCNT = 1; // 1 byte message,
I2caRegs.I2CDXR = VC3_HI; // target here: pointer to VC6_HI register
// Send start as master transmitter
I2caRegs.I2CMDR.all = 0x6620; // transmitter mode
while(I2caRegs.I2CSTR.bit.ARDY == 0); // wait for access ready condition

// Read 1st byte
I2caRegs.I2CCNT = 1; // read 1 byte
I2caRegs.I2CMDR.all = 0x6C20; //receiver mode
// while(I2caRegs.I2CSTR.bit.RRDY == 0); // wait for 1st byte

Voltage_regs[2] = I2caRegs.I2CDRR << 8; // read upper 8 Bit (integers)
// RRDY is automatically cleared by read of I2CDRR
// Send START and set pointer to VC6_LO - register
I2caRegs.I2CCNT = 1; // 1 byte message,
I2caRegs.I2CDXR = VC3_LO; // target here: pointer to VC6_LO register
// Send start as master transmitter
I2caRegs.I2CMDR.all = 0x6620; // transmitter mode
while(I2caRegs.I2CSTR.bit.ARDY == 0); // wait for access ready condition
// Read 2sd byte
I2caRegs.I2CCNT = 1; // read 1 byte
I2caRegs.I2CMDR.all = 0x6C20; // receiver mode
// while(I2caRegs.I2CSTR.bit.RRDY == 0); // wait for 2nd byte

Voltage_regs[2] += I2caRegs.I2CDRR; // read lower 8 Bit (fractions)

//Read voltage of cell 4 (cell 4 in the battery string is cell 6 of the monitoring IC)
// Send START and set pointer to VC7_HI - register
I2caRegs.I2CCNT = 1; // 1 byte message,
I2caRegs.I2CDXR = VC5_HI; // target here: pointer to VC7_HI register
// Send start as master transmitter
I2caRegs.I2CMDR.all = 0x6620; // transmitter mode
while(I2caRegs.I2CSTR.bit.ARDY == 0); // wait for access ready condition

// Read 1st byte
I2caRegs.I2CCNT = 1; // read 1 byte
I2caRegs.I2CMDR.all = 0x6C20; //receiver mode
// while(I2caRegs.I2CSTR.bit.RRDY == 0); // wait for 1st byte

Voltage_regs[3] = I2caRegs.I2CDRR << 8; // read upper 8 Bit (integers)
// RRDY is automatically cleared by read of I2CDRR
// Send START and set pointer to VC7_LO - register
I2caRegs.I2CCNT = 1; // 1 byte message,
I2caRegs.I2CDXR = VC5_LO; // target here: pointer to VC7_LO register
// Send start as master transmitter
I2caRegs.I2CMDR.all = 0x6620; // transmitter mode
while(I2caRegs.I2CSTR.bit.ARDY == 0); // wait for access ready condition

// Read 2sd byte
I2caRegs.I2CCNT = 1; // read 1 byte
I2caRegs.I2CMDR.all = 0x6C20; // receiver mode
// while(I2caRegs.I2CSTR.bit.RRDY == 0); // wait for 2nd byte

Voltage_regs[3] += I2caRegs.I2CDRR; // read lower 8 Bit (fractions)

I2caRegs.I2CCNT = 1; // 1 byte message,
I2caRegs.I2CDXR = CC_HI; // target here: pointer to VC7_HI register
// Send start as master transmitter
I2caRegs.I2CMDR.all = 0x6620; // transmitter mode
// while(I2caRegs.I2CSTR.bit.ARDY == 0); // wait for access ready condition

// Read 1st byte
I2caRegs.I2CCNT = 1; // read 1 byte
I2caRegs.I2CMDR.all = 0x6C20; //receiver mode
// while(I2caRegs.I2CSTR.bit.RRDY == 0); // wait for 1st byte

I_regs = I2caRegs.I2CDRR << 8; // read upper 8 Bit (integers)
// RRDY is automatically cleared by read of I2CDRR
// Send START and set pointer to VC7_LO - register
I2caRegs.I2CCNT = 1; // 1 byte message,
I2caRegs.I2CDXR = CC_LO; // target here: pointer to VC7_LO register
// Send start as master transmitter
I2caRegs.I2CMDR.all = 0x6620; // transmitter mode
// while(I2caRegs.I2CSTR.bit.ARDY == 0); // wait for access ready condition

// Read 2sd byte
I2caRegs.I2CCNT = 1; // read 1 byte
I2caRegs.I2CMDR.all = 0x6C20; // receiver mode
// while(I2caRegs.I2CSTR.bit.RRDY == 0); // wait for 2nd byte

I_regs += I2caRegs.I2CDRR; // read lower 8 Bit (fractions)

I_cal = I_regs*CC_LCB_voltage;// calculate the actual value of current flow through
I_cal = I_cal/resistor_value;

//I_cal = 1600.00f;
current_pack=-I_cal/1000.00f;// because CC_LCB voltage is in micro-volt

// if ((abs(current_pack))<=0.20f){current_pack = 0.00f;}

for(i=0;i<k;i++)
{
Voltage_Cell[i]=Voltage_regs[i]*voltage_gain;
Voltage_Cell[i]=Voltage_Cell[i]*0.000001f;
Voltage_Cell[i]=Voltage_Cell[i]+voltage_offset;
}
/* // Send START and set pointer to SYS_CTRL2 - register
I2caRegs.I2CCNT = 1; // 1 byte message,
I2caRegs.I2CDXR = SYS_CTRL2; // target here: pointer to SYS_CTRL2 register
// Send start as master transmitter
I2caRegs.I2CMDR.all = 0x6620; // transmitter mode
while(I2caRegs.I2CSTR.bit.ARDY == 0); // wait for access ready condition
// Read 1st byte
I2caRegs.I2CCNT = 1; // read 1 byte
I2caRegs.I2CMDR.all = 0x6C20; //receiver mode
while(I2caRegs.I2CSTR.bit.RRDY == 0); // wait for 1st byte
SYS_CTRL2_register = I2caRegs.I2CDRR ; // read 8 Bit (integers)
*/
} // end of Update_Cell_Voltage_Current function
void I2CA_Init(void)
{
I2caRegs.I2CMDR.bit.IRS = 0; // Reset the I2C module
// I2C slave address register
I2caRegs.I2CSAR = BQ76940_SLAVE;
// I2C Prescale Register
I2caRegs.I2CPSC.all = 14; // Internal I2C module clock = SYSCLK/(PSC +1)
// = 10 MHz

// I2caRegs.I2CCLKL = 95; // Tmaster = (PSC +1)[ICCL + 5 + ICCH + 5] / 150MHz
// I2caRegs.I2CCLKH = 95; // Tmaster = 10 [ICCL + ICCH + 10] / 150 MHz
// d = 5 for IPSC >1

// for I2C 50 kHz:
// Tmaster = 20 µs *150 MHz / 10 = 200 = (ICCL + ICCH +10)
// ICCL + ICCH = 190
// ICCL = ICH = 190/2 = 95

I2caRegs.I2CCLKL = 45;
I2caRegs.I2CCLKH = 45; // for I2C 100 kHz:
// Tmaster = 10 µs *150 MHz / 10 = 100 = (ICCL + ICCH + 10)
// ICCL + ICCH = 90
// ICCL = ICH = 90/2 = 45

I2caRegs.I2CMDR.bit.IRS = 1; // Take I2C out of reset

} // End of setup I2CA_Init