CCS/MSP432P401R: Transmit a string as an acknowledgement after recieving data from UART

r venkatesh

Part Number: MSP432P401R

Tool/software: Code Composer Studio

hello,

Im trying to send an acknowledgement after recieving the data but am not able to send a string after reception. ive taken my base code from the uart echo example and tried to add a string by removing the EUSCI_A0->RXBUF;in the below code. But only see '@' a lot in the terminal . Can you please help me out with this as im very much new to this .

// Echo the received character back
EUSCI_A0->TXBUF = EUSCI_A0->RXBUF;
}
}

over 7 years ago

0 r venkatesh over 7 years ago

Intellectual 770 points

r venkatesh said:

Part Number: MSP432P401R

Tool/software: Code Composer Studio

hello,

Im trying to send an acknowledgement after recieving the data but am not able to send a string after reception. ive taken my base code from the uart echo example and tried to add a string by removing the EUSCI_A0->RXBUF;in the below code. But only see '@' a lot in the terminal . Can you please help me out with this as im very much new to this .

// Echo the received character back
EUSCI_A0->TXBUF = EUSCI_A0->RXBUF;
}
}

// MSP432P401 Demo - eUSCI_A0 UART echo at 9600 baud using BRCLK = 12MHz
//
// Description: This demo echoes back characters received via a PC serial port.
// SMCLK/ DCO is used as a clock source and the device is put in LPM0
// The auto-clock enable feature is used by the eUSCI and SMCLK is turned off
// when the UART is idle and turned on when a receive edge is detected.
// Note that level shifter hardware is needed to shift between RS232 and MSP
// voltage levels.
//
// The example code shows proper initialization of registers
// and interrupts to receive and transmit data.
//
// MSP432P401
// -----------------
// /|\| |
// | | |
// --|RST |
// | |
// | |
// | P1.3/UCA0TXD|----> PC (echo)
// | P1.2/UCA0RXD|<---- PC
// | |
//
// William Goh
// Texas Instruments Inc.
// June 2016 (updated) | June 2014 (created)
// Built with CCSv6.1, IAR, Keil, GCC
//******************************************************************************
#include "msp.h"

int main(void)
{
WDT_A->CTL = WDT_A_CTL_PW | // Stop watchdog timer
WDT_A_CTL_HOLD;

CS->KEY = CS_KEY_VAL; // Unlock CS module for register access
CS->CTL0 = 0; // Reset tuning parameters
CS->CTL0 = CS_CTL0_DCORSEL_3; // Set DCO to 12MHz (nominal, center of 8-16MHz range)
CS->CTL1 = CS_CTL1_SELA_2 | // Select ACLK = REFO
CS_CTL1_SELS_3 | // SMCLK = DCO
CS_CTL1_SELM_3; // MCLK = DCO
CS->KEY = 0; // Lock CS module from unintended accesses

// Configure UART pins
P1->SEL0 |= BIT2 | BIT3; // set 2-UART pin as secondary function

// Configure UART
EUSCI_A0->CTLW0 |= EUSCI_A_CTLW0_SWRST; // Put eUSCI in reset
EUSCI_A0->CTLW0 = EUSCI_A_CTLW0_SWRST | // Remain eUSCI in reset
EUSCI_B_CTLW0_SSEL__SMCLK; // Configure eUSCI clock source for SMCLK
// Baud Rate calculation
// 12000000/(16*9600) = 78.125
// Fractional portion = 0.125
// User's Guide Table 21-4: UCBRSx = 0x10
// UCBRFx = int ( (78.125-78)*16) = 2
EUSCI_A0->BRW = 78; // 12000000/16/9600
EUSCI_A0->MCTLW = (2 << EUSCI_A_MCTLW_BRF_OFS) |
EUSCI_A_MCTLW_OS16;

EUSCI_A0->CTLW0 &= ~EUSCI_A_CTLW0_SWRST; // Initialize eUSCI
EUSCI_A0->IFG &= ~EUSCI_A_IFG_RXIFG; // Clear eUSCI RX interrupt flag
EUSCI_A0->IE |= EUSCI_A_IE_RXIE; // Enable USCI_A0 RX interrupt

// Enable global interrupt
__enable_irq();

// Enable eUSCIA0 interrupt in NVIC module
NVIC->ISER[0] = 1 << ((EUSCIA0_IRQn) & 31);

// Enable sleep on exit from ISR
SCB->SCR |= SCB_SCR_SLEEPONEXIT_Msk;

// Ensures SLEEPONEXIT occurs immediately
__DSB();

// Enter LPM0
__sleep();
__no_operation(); // For debugger
}

// UART interrupt service routine
void EUSCIA0_IRQHandler(void)
{
if (EUSCI_A0->IFG & EUSCI_A_IFG_RXIFG)
{
// Check if the TX buffer is empty first
while(!(EUSCI_A0->IFG & EUSCI_A_IFG_TXIFG));

// Echo the received character back
EUSCI_A0->TXBUF = EUSCI_A0->RXBUF;
}
// EUSCI_A0->TXBUF = 'a';
}

0 Stefan Schauer over 7 years ago in reply to r venkatesh

TI__Guru 61091 points

Based on the screenshot or your Terminal it looks like you have selected

9600 Baud - 7 Data bits - 1 Stop Bit - No Parity - Handshake on RTS

But Example uses:

9600 Baud - 8 Data bits - 1 Stop Bit - No Parity - No Handshake

Esp. the data bits can generate the seen issue.

Best regards,

Stefan

If I had answered to your question, please mark this post as Resolved.

0 r venkatesh over 7 years ago in reply to Stefan Schauer

Intellectual 770 points

Hello Stefen,

Thank you for your reply.

As you can see that it has solved the random @ issue now i face an other one. Can you please help me so that the acknowledgement for eg in the code ive used B as acknowledgement. i wanted to use it once per transmission but you can see its continuously transmitting . below is the code and screenshot. Thanks in advance.

#include "msp.h"

int main(void)
{
WDT_A->CTL = WDT_A_CTL_PW | // Stop watchdog timer
WDT_A_CTL_HOLD;

// Configure UART pins
P1->SEL0 |= BIT2 | BIT3; // set 2-UART pin as secondary function

EUSCI_A0->CTLW0 &= ~EUSCI_A_CTLW0_SWRST; // Initialize eUSCI
EUSCI_A0->IFG &= ~EUSCI_A_IFG_RXIFG; // Clear eUSCI RX interrupt flag
EUSCI_A0->IE |= EUSCI_A_IE_RXIE; // Enable USCI_A0 RX interrupt

// Enable global interrupt
__enable_irq();

// Enable eUSCIA0 interrupt in NVIC module
NVIC->ISER[0] = 1 << ((EUSCIA0_IRQn) & 31);

// Enable sleep on exit from ISR
SCB->SCR |= SCB_SCR_SLEEPONEXIT_Msk;

// Ensures SLEEPONEXIT occurs immediately
__DSB();

// Enter LPM0
__sleep();
__no_operation(); // For debugger
}

// UART interrupt service routine
void EUSCIA0_IRQHandler(void)
{
// if (EUSCI_A0->IFG & EUSCI_A_IFG_RXIFG)
// {
// Check if the TX buffer is empty first
// while(!(EUSCI_A0->IFG & EUSCI_A_IFG_TXIFG));

// Echo the received character back
//EUSCI_A0->TXBUF = EUSCI_A0->RXBUF;
// }
EUSCI_A0->TXBUF = 'B';
}

0 Stefan Schauer over 7 years ago in reply to r venkatesh

TI__Guru 61091 points

Hi,

you get continuous calls into the UART interrupt service handler because the RX interrupt flag does not get cleared.

This flag gets cleared automatically by reading the EUSCI_A0->RXBUF or by clearing the flag.

Note: before putting data into the TXBUF register it is a good practice to also check if the buffer is free.

So the simplified interrupt service handler function just sending back a fixed char once any character is received can look like this:

// UART interrupt service routine
void EUSCIA0_IRQHandler(void)
{
  volatile  uint8_t temp;   // volatile temp register to avoid optimizing

  if (EUSCI_A0->IFG & EUSCI_A_IFG_RXIFG)
  {
    // Either read RXBUF or clear RX IFG
    temp = EUSCI_A0->RXBUF;
    //EUSCI_A0->IFG &= ~EUSCI_A_IFG_RXIFG;

    //Check if the TX buffer is empty first
    while(!(EUSCI_A0->IFG & EUSCI_A_IFG_TXIFG));

    //EUSCI_A0->TXBUF = EUSCI_A0->RXBUF;
    EUSCI_A0->TXBUF = 'B';
  }
}

0 r venkatesh over 7 years ago in reply to Stefan Schauer

Intellectual 770 points

Thanks for the reply stefen. this has solved my issue. Now im able send and receive acknowledgement. Thnaks a ton

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CCS/MSP432P401R: Transmit a string as an acknowledgement after recieving data from UART