MSP430F5438A REV D UART register read problem

Nikhil Magdum

Other Parts Discussed in Thread: MSP430F5438A

Hello,

I am working with MSP430F5438A REV D on Experimenters board by TI. I want to do serial communication using USCI_A1 module in polling mode (by checking UCBUSY bit in UCA1STAT register). The baud rate is 9600 with ACLK= 32.768KHz. Here is the code for the the same. My IDE is Code Composer Studio v5.2

#include <msp430f5438a.h>

void main(void)
{
   WDTCTL = WDTPW + WDTHOLD;       // Stop watchdog timer

   P5DIR |= 0x01;                   // Set P1.0 to output direction
   P1DIR |= 0x01;                             // Set P1.0 to output direction
   UCA1CTL1 |= (1<<0);               // reset the UART and hold in logic high state

   UCA1MCTL &= ~(1<<0);           // UCOS16 = 0 for low baud rate
   P5SEL |= (1<<6);                        // P5.6 as TxD
   P5SEL |= (1<<7);                       // P5.7 as RxD

    /* UCA1CTLW0 = 0x4120; */
   UCA1CTL1 |= 0x41;               // clock source for BRclk= ACLK
   UCA1CTL0 |= 0x20;               // parity disable, MSB first, 8bit data, 1 stop bit, UART mode, Asynchronous mode
   UCA1BR0 = 3;                         // for baud rate of 9600 with ACLK=32.768KHz
   UCA1BR1 = 3;
   UCA1IE |= 0x03;                      // transmit and receive interrupt enable

   UCA1CTL1 &= ~(1<<0);           // release USCI for operation
   while(1)
   {
       UCA1TXBUF=65;               // start transmitting the data
       while(UCA1STAT & 0x01); // wait for transmit complete
       volatile unsigned int i;         // volatile to prevent optimization

               P1OUT ^= 0x01;           // Toggle P1.0 using exclusive-OR

               i = 10000;           // SW Delay
               do i--;
               while(i != 0);
   }
}

But I am not able to do communication. The program gets stuck at line

while(UCA1STAT & 0x01);

While debugging, in registers window I get error as "Cannot Read the register" which are related to USCI_A1 UART. They are memory mapped registers.In some other forum related to OMAP I read that it can be a problem with GEL file.

Is it so? Or any problem with code? Or any problem with REV D series? What can be the problem?

over 12 years ago

0 luis.lopez over 12 years ago

Expert 1050 points

In my firmwares, I always fill the UCA1TXBUF after the while, no before, because that means that any execution are using the UART. That's it:

while(UCA1STAT & 0x01); // wait for transmit complete wait until UART is not busy

UCA1TXBUF=65; // start transmitting the data

0 Jens-Michael Gross over 12 years ago in reply to luis.lopez

Guru 227245 points

Luis L��pez said:
In my firmwares, I always fill the UCA1TXBUF after the while, no before, because that means that any execution are using the UART. That's it:

It will indeed work, but it makes the double-buffering of the USCI worthless, reducing maximum throughput.
The good thing about the double.buffering is, that you can fetch the next data byte and store it in TXBUF while the previous byte is still being sent. So you get seamless transfer with maximum speed.
If you read or write SD cards through SPI, this makes the difference between 2MB/s and 0.5MB/s throughput.

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MSP430F5438A REV D UART register read problem