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//****************************************************************************** // MSP430G2xx2 Demo - Timer_A, Ultra-Low Pwr UART 9600 Echo, 32kHz ACLK // // Description: Use Timer_A CCR0 hardware output modes and SCCI data latch // to implement UART function @ 9600 baud. Software does not directly read and // write to RX and TX pins, instead proper use of output modes and SCCI data // latch are demonstrated. Use of these hardware features eliminates ISR // latency effects as hardware insures that output and input bit latching and // timing are perfectly synchronised with Timer_A regardless of other // software activity. In the Mainloop the UART function readies the UART to // receive one character and waits in LPM3 with all activity interrupt driven. // After a character has been received, the UART receive function forces exit // from LPM3 in the Mainloop which configures the port pins (P1 & P2) based // on the value of the received byte (i.e., if BIT0 is set, turn on P1.0).
// ACLK = TACLK = LFXT1 = 32768Hz, MCLK = SMCLK = default DCO // //* An external watch crystal is required on XIN XOUT for ACLK *// // // MSP430G2xx2 // ----------------- // /|\| XIN|- // | | | 32kHz // --|RST XOUT|- // | | // | CCI0B/TXD/P1.1|--------> // | | 9600 8N1 // | CCI0A/RXD/P1.2|<-------- // // D. Dang // Texas Instruments Inc. // December 2010 // Built with CCS Version 4.2.0 and IAR Embedded Workbench Version: 5.10 //******************************************************************************
//------------------------------------------------------------------------------ // Global variables used for full-duplex UART communication //------------------------------------------------------------------------------ unsigned int txData; // UART internal variable for TX unsigned char rxBuffer; // Received UART character
// Echo received character TimerA_UART_tx(rxBuffer); } } //------------------------------------------------------------------------------ // Function configures Timer_A for full-duplex UART operation //------------------------------------------------------------------------------ void TimerA_UART_init(void) { TACCTL0 = OUT; // Set TXD Idle as Mark = '1' TACCTL1 = SCS + CM1 + CAP + CCIE; // Sync, Neg Edge, Capture, Int TACTL = TASSEL_2 + MC_2; // SMCLK, start in continuous mode } //------------------------------------------------------------------------------ // Outputs one byte using the Timer_A UART //------------------------------------------------------------------------------ void TimerA_UART_tx(unsigned char byte) { while (TACCTL0 & CCIE); // Ensure last char got TX'd TACCR0 = TAR; // Current state of TA counter TACCR0 += UART_TBIT; // One bit time till first bit TACCTL0 = OUTMOD0 + CCIE; // Set TXD on EQU0, Int txData = byte; // Load global variable txData |= 0x100; // Add mark stop bit to TXData txData <<= 1; // Add space start bit }
//------------------------------------------------------------------------------ // Prints a string over using the Timer_A UART //------------------------------------------------------------------------------ void TimerA_UART_print(char *string) { while (*string) { TimerA_UART_tx(*string++); } } //------------------------------------------------------------------------------ // Timer_A UART - Transmit Interrupt Handler //------------------------------------------------------------------------------ #pragma vector = TIMER0_A0_VECTOR __interrupt void Timer_A0_ISR(void) { static unsigned char txBitCnt = 10;
