TMS320F28335: DSP serial port communication ossie

Hi team,

Here's an issue from the customer may need your help:

The initial state of the serial port Tx side of the host is +6V, and when the serial port is started, the Tx side changes +6V to -6V, which causes the DSP28335 serial port to fail to communicate.

After testing, it's found that ScicRegs.SCICTL1.all = 0x0003; and ScicRegs.SCICTL1.all = 0x0023; this register needs to be reprogramed , then to communicate and receive data normally. The 28335 does not receive data after the host has transmitted data, the following is the serial initialization function:

void Sci_Init(void)
{
EALLOW;
GpioCtrlRegs.GPBPUD.bit.GPIO62 = 0; // Enable pull-up for GPIO62 (SCIRXDC)
GpioCtrlRegs.GPBPUD.bit.GPIO63 = 0; // Enable pull-up for GPIO63 (SCITXDC)

GpioCtrlRegs.GPBQSEL2.bit.GPIO62 = 3; // Asynch input GPIO62 (SCIRXDC)

GpioCtrlRegs.GPBMUX2.bit.GPIO62 = 1; // Configure GPIO62 for SCIRXDC operation
GpioCtrlRegs.GPBMUX2.bit.GPIO63 = 1; // Configure GPIO63 for SCITXDC operation
EDIS;

ScicRegs.SCICCR.all = 0x0007;
ScicRegs.SCICTL1.all = 0x0003; // enable TX, RX, internal SCICLK,
ScicRegs.SCICTL2.all = 0x0003;
ScicRegs.SCICTL2.bit.TXINTENA = 0;
ScicRegs.SCICTL2.bit.RXBKINTENA =1;

ScicRegs.SCIHBAUD = 0x0000; // 115200 baudrate @LSPCLK = 37.5MHz.
ScicRegs.SCILBAUD = 0x0028;

ScicRegs.SCICTL1.all = 0x0023;
ScicRegs.SCIFFTX.all = 0x8000; // Disabled FIFO

EALLOW;
PieVectTable.SCIRXINTC = &ScicRx; //Place the SCIC interrupt sub-program address entry into the interrupt vector table
EDIS;
PieCtrlRegs.PIECTRL.bit.ENPIE = 1; // Enable PIE vector table
PieCtrlRegs.PIEIER8.bit.INTx5 = 1; // Turn on Group 8 interrupt 5: SCICRX interrupt IER |= M_INT8;

}

If the Tx side of the host serial port has an initial state of -6V, the serial port of the 28335 does not become stuck when the host starts the serial port. The reason should be the initial state of the host serial port +6V, start the serial port, change to -6V, affecting the ScicRegs.SCICTL1 of the 28335 to control register.  Online debug monitoring, the value of this register is not changed, but must be re-assigned to communicate properly. The customer would like to know what' the reason for that. 

Could you help check this case? Thanks.

Best Regards,

Cherry