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Imants Pulkstenis
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/* --COPYRIGHT--,BSD_EX
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* Copyright (c) 2012, Texas Instruments Incorporated
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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*
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* * Neither the name of Texas Instruments Incorporated nor the names of
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* its contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
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* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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*******************************************************************************
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*
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* MSP430 CODE EXAMPLE DISCLAIMER
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*
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* MSP430 code examples are self-contained low-level programs that typically
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* demonstrate a single peripheral function or device feature in a highly
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* concise manner. For this the code may rely on the device's power-on default
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* register values and settings such as the clock configuration and care must
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* be taken when combining code from several examples to avoid potential side
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* effects. Also see www.ti.com/grace for a GUI- and www.ti.com/msp430ware
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* for an API functional library-approach to peripheral configuration.
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*
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* --/COPYRIGHT--*/
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//******************************************************************************
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// MSP430F20xx Demo - Timer_A, Ultra-Low Pwr UART 2400 Echo, 32kHz ACLK
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//
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// Description: Use Timer_A CCR0 hardware output modes and SCCI data latch
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// to implement UART function @ 2400 baud. Software does not directly read and
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// write to RX and TX pins, instead proper use of output modes and SCCI data
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// latch are demonstrated. Use of these hardware features eliminates ISR
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// latency effects as hardware insures that output and input bit latching and
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// timing are perfectly synchronised with Timer_A regardless of other
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// software activity. In the Mainloop the UART function readies the UART to
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// receive one character and waits in LPM3 with all activity interrupt driven.
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// After a character has been received, the UART receive function forces exit
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// from LPM3 in the Mainloop which echo's back the received character.
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// ACLK = TACLK = LFXT1 = 32768Hz, MCLK = SMCLK = default DCO
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// //* An external watch crystal is required on XIN XOUT for ACLK *//
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//
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// MSP430F20xx
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// -----------------
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// /|\| XIN|-
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// | | | 32kHz
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// --|RST XOUT|-
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// | |
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// | CCI0B/TXD/P1.5|-------->
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// | | 2400 8N1
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// | CCI0A/RXD/P1.1|<--------
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//
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#define RXD 0x02 // RXD on P1.1
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#define TXD 0x20 // TXD on P1.5
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// Conditions for 2400 Baud SW UART, ACLK = 32768
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#define Bitime_5 0x06 // ~ 0.5 bit length + small adjustment
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#define Bitime 0x0E // 427us bit length ~ 2341 baud
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unsigned int RXTXData;
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unsigned char BitCnt;
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void TX_Byte (void);
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void RX_Ready (void);
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// M. Buccini / L. Westlund
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// Texas Instruments Inc.
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// October 2005
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// Built with CCE Version: 3.2.0 and IAR Embedded Workbench Version: 3.40A
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//******************************************************************************
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#include <msp430.h>
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int main (void)
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{
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WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer
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CCTL0 = OUT; // TXD Idle as Mark
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TACTL = TASSEL_1 + MC_2; // ACLK, continuous mode
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P1SEL = TXD + RXD; //
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P1DIR = TXD; //
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// Mainloop
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for (;;)
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{
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RX_Ready(); // UART ready to RX one Byte
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__bis_SR_register(LPM3_bits + GIE); // Enter LPM3 w/ interr until char RXed
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TX_Byte(); // TX Back RXed Byte Received
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}
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}
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// Function Transmits Character from RXTXData Buffer
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void TX_Byte (void)
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{
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BitCnt = 0xA; // Load Bit counter, 8data + ST/SP
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while (CCR0 != TAR) // Prevent async capture
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CCR0 = TAR; // Current state of TA counter
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CCR0 += Bitime; // Some time till first bit
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RXTXData |= 0x100; // Add mark stop bit to RXTXData
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RXTXData = RXTXData << 1; // Add space start bit
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CCTL0 = CCIS0 + OUTMOD0 + CCIE; // TXD = mark = idle
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while ( CCTL0 & CCIE ); // Wait for TX completion
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}
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// Function Readies UART to Receive Character into RXTXData Buffer
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void RX_Ready (void)
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{
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BitCnt = 0x8; // Load Bit counter
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CCTL0 = SCS + OUTMOD0 + CM1 + CAP + CCIE; // Sync, Neg Edge, Cap
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}
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// Timer A0 interrupt service routine
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#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
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#pragma vector=TIMERA0_VECTOR
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__interrupt void Timer_A (void)
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#elif defined(__GNUC__)
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void __attribute__ ((interrupt(TIMERA0_VECTOR))) Timer_A (void)
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#else
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#error Compiler not supported!
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#endif
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{
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CCR0 += Bitime; // Add Offset to CCR0
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// TX
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if (CCTL0 & CCIS0) // TX on CCI0B?
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{
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if ( BitCnt == 0)
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CCTL0 &= ~ CCIE; // All bits TXed, disable interrupt
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else
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{
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CCTL0 |= OUTMOD2; // TX Space
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if (RXTXData & 0x01)
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CCTL0 &= ~ OUTMOD2; // TX Mark
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RXTXData = RXTXData >> 1;
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BitCnt --;
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}
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}
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// RX
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else
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{
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if( CCTL0 & CAP ) // Capture mode = start bit edge
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{
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CCTL0 &= ~ CAP; // Switch from capture to compare mode
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CCR0 += Bitime_5;
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}
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else
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{
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RXTXData = RXTXData >> 1;
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if (CCTL0 & SCCI) // Get bit waiting in receive latch
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RXTXData |= 0x80;
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BitCnt --; // All bits RXed?
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if ( BitCnt == 0)
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//>>>>>>>>>> Decode of Received Byte Here <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
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{
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CCTL0 &= ~ CCIE; // All bits RXed, disable interrupt
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__bic_SR_register_on_exit(LPM3_bits); // Clear LPM3 bits from 0(SR)
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}
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//>>>>>>>>>> Decode of Received Byte Here <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
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}
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}
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}
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