G2553 Hardware UART "Hello World" Example

[username 198]

Howdy all, sorry I neglected this post. I updated the code for the rev 1.5 and made some improvements. My coding skills hopefully have improved abit over the last year. I'm avoiding interrupts & low power modes for simplicity. This code is meant for beginners

[roadrunner84 466]

The routines by Fred and gwdeveloper are essentially the same, except for Fred's routine doing busy chacking before sending instead of after.

I do prefer for loops in this case, since you're using a counter with initialisation, condition and increment.

TX( char* string )
{
  int pointer;
  for( pointer = 0; string[pointer] != '\0' /* && pointer < 50 */; pointer++)
  {
    while (!(IFG2&UCA0TXIFG)); // USCI_A0 TX buffer ready?
    UCA0TXBUF = string[pointer];
  }
} 

[Fred 453]

So many ways to do the same thing. All good. Let's not get into a argument on coding style though!

 

Anyone want to write an obfuscated version? You know the sort of thing. All crammed onto one line. Saves you 2 bytes and 10 microseconds but is bordering on unreadable and unmaintainable. 

[roadrunner84 466]

void TX(char*s){do while(!(IFG2&UCA0TXIFG));while(UCA0TXBUF=*s++);}

something like this? :twisted:

void TX(char*s){int p;do while(!(IFG2&UCA0TXIFG));while(UCA0TXBUF=s[p++]);}

Or for the sake of unreadability, use upper case i and lower case L as variables:

void TX(char*l){int I;do while(!(IFG2&UCA0TXIFG));while(UCA0TXBUF=l[i++]);}

[Fred 453]

Pretty good. I particularly like the first one where I believe you modify the pointer that's passed in, potentially causing unexpected behaviour in code that follows. I've no idea if any of those would work or have serious bugs, so I'd call that a success!

[gwdeveloper 275]

LOL, no arguments here. That's what the community is here for, right? ...to confuse the heck out of each other sometimes. I'm still waiting for oPossum to show us how it's really done. :!!!:

[roadrunner84 466]

No, it will work. C cannot pass anything by reference, so instad a pointer to the concerning data is passed. This pointer is a copy of the pointer used in the calling code. So now there are two pointers to the same string of characters in memory; one in the calling code and one in the local scope of the TX function. Since the local variable is destroyed (popped off of the stack or just abandon the value in the general purpose register) after TX returns, there is no harm done. So yeah, TX loses the start of the string pointer as it progresses over the string, but the calling code has its own version of that pointer, which is untouched and still points to the start of the string.

[mahojazz 0]

Hi i do have some issue using the TI hardware UART on launchpad. Somehow, i can't communicate at 115200 baud rate but 9600 baud works fine. What should i set for DCOCTL, BCSCTL1, UCA0CTL1, UCA0BR0 and UCA0BR1 if i want to have a system clock of 16MHz, hardware UART.

I am using RealTerm to communicate. Setting port to Baud 115200, no hardware flow control, 8N1

 

 Right now, my settings are as follows:

DCOCTL = CALDCO_16MHz;

BCSCTL1= CALBC1_16MHz;

UCA0CTL1 = UCSSEL_2;

UCA0BR0 = 125;

UCA0BR1 = 0;

UCA0MCTL = 0;

 

Thanks alot

 

 

Eric

[roadrunner84 466]

This is a known problem. It's not a problem in the chip itself, butg rather in the programmer part. If you have a FTDI TTL UART cable hanging around you could try and use that one instead, it should work then.

[oPossum 1,083]

The MSP430 launchpad application UART is limited to 1200, 2400, 4800 or 9600 bps. It won't run at any other speeds.

[oPossum 1,083]

I'm still waiting for oPossum to show us how it's really done.

 

#include <msp430.h>
#include <stdint.h>

const unsigned RXD = BIT1;
const unsigned TXD = BIT2;
const unsigned SW2 = BIT3;

const unsigned long smclk_freq = 16000000;      // SMCLK frequency in hertz
const unsigned long bps = 9600;                 // Async serial bit rate


// Output char to UART
static inline void putc(const unsigned c) { while(UCA0STAT & UCBUSY); UCA0TXBUF = c; }

// Output string to UART
void puts(const char *s) { while(*s) putc(*s++); }

// CR LF
void crlf(void) { puts("\r\n"); }

// Output binary array to UART
void putb(const uint8_t *b, unsigned n) { do putc(*b++); while(--n); }

// Print unsigned int
void print_u(unsigned x)
{
    static const unsigned dd[] = { 10000, 1000, 100, 10, 1 };
    const unsigned *dp = dd; unsigned d;
    if(x) { while(x < *dp) ++dp;
        do { d = *dp++; char c = '0'; while(x >= d) ++c, x -= d; putc(c); } while(!(d & 1));
    } else putc('0');
}

// Print signed int
void print_i(const int x) { if(x < 0) putc('-'); print_u((x < 0) ? -x : x); }

// Print hex nibble
static inline void puth(const unsigned x) { putc("0123456789ABCDEF"[x & 15]); }

// Print hex byte
void print_hb(const unsigned x) { puth(x >> 4); puth(x); }

// Print hex word
void print_hw(const unsigned x) { print_hb(x >> 8); print_hb(x); }

void main(void)
{
    WDTCTL = WDTPW + WDTHOLD;                   // No watchdog reset
                                                //
    DCOCTL = 0;                                 // Run at 16 MHz
    BCSCTL1 = CALBC1_16MHZ;                     //
    DCOCTL  = CALDCO_16MHZ;                     //
                                                //
    P1DIR = ~(RXD | SW2);                       // Setup I/O for UART and switch
    P1OUT = P1REN  = RXD | SW2;                 //
    P1SEL = P1SEL2 = RXD | TXD;                 //
                                                //
    const unsigned long brd = (smclk_freq + (bps >> 1)) / bps; // Bit rate divisor
    UCA0CTL1 = UCSWRST;                         // Hold USCI in reset to allow configuration
    UCA0CTL0 = 0;                               // No parity, LSB first, 8 bits, one stop bit, UART (async)
    UCA0BR1 = (brd >> 12) & 0xFF;               // High byte of whole divisor
    UCA0BR0 = (brd >> 4) & 0xFF;                // Low byte of whole divisor
    UCA0MCTL = ((brd << 4) & 0xF0) | UCOS16;    // Fractional divisor, oversampling mode                
    UCA0CTL1 = UCSSEL_2;                        // Use SMCLK for bit rate generator, release reset                                              

    for(; {                                   //
        int n = 1;                              //
        do (P1IN & BIT3) ? --n : (n = 5000); while(n);
        do (P1IN & BIT3) ? n = 5000 : --n; while(n);
        puts("Poke me with a Stick\r\n");       //
        for(n = -5; n <= 5;) print_i(n++), putc(' '); crlf();
        n = 0xDEAD; print_hw(n); putc(' ');     //
        n += 0xE042; print_hw(n); crlf();       //
        crlf();                                 //
    }                                           //
 }                                              //
 

[gwdeveloper 275]

LMAO! I knew it. I've gotten better at reading your code. Man, that's great!

[username 198]

Pretty darn awesome opossum! You by chance got a big archive somewhere of all your awesome msp430 code?

[mahojazz 0]

thanks alot. 

[yyrkoon 250]

 

        do (P1IN & BIT3) ? --n : (n = 5000); while(n);
        do (P1IN & BIT3) ? n = 5000 : --n; while(n)

 

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