The msp430f2013 does not have UART ports. So I found that a software UART can be created and I followed the code from J H Davies book. As I have mentioned in the question, i am basically trying to interface a GSM modem to the MSP. My question are'
1. Is it possible to do this on a software UART?
2. Once I have compiled the software UART program, how do I check it? Can I do this on Hyperterminal or putty?
I have read the various discussions on this forum about software UART but my doubt is not cleared.
The code i used for software UART is below.
#include <io430x20x3.h> // Header file for this device
#include <stdint.h> // Integers of defined sizes
#include "uartlib.h" // Library for software UART
#define LED P1OUT_bit.P1OUT_0 // Output pin for LED (active high)
uint8_t RXBUF; // Buffer for received byte
uint8_t TXBUF; // Buffer for byte to transmit#define BITTIME ((1000000 + 4800)/9600) // Cycles of TACLK per bit , 1MHz
#define HALFTIME (BITTIME/2) // Cycles for half a bit
void UARTSetUp ( void )
{
TACTL = TASSEL_2 | MC_2; // TACLK = SMCLK = 1MHz
TACCTL0 = OUT | OUTMOD_0 | CCIFG;
TACCTL1 = CM_2 | CCIS_1 | SCS | CAP | OUTMOD_0 | CCIE;
RXIFG = 0; // Buffer empty , no byte received
TXIFG = 1; // Buffer empty , ready to accept TX
}
//----------------------------------------------------------------------
// Write byte to TXBUF; clears flag , starts transmitter if necessary
//----------------------------------------------------------------------
void WriteTXBUF ( const uint8_t TXData)
{
TXBUF = TXData; // Transfer data to buffer
TXIFG = 0; // Clear interrupt flag
TACCTL0_bit. CCIE = 1; // Enable interrupts if inactive ,
} // no effect if already running
//----------------------------------------------------------------------
// Read byte from RXBUF; clears flag
//----------------------------------------------------------------------
uint8_t ReadRXBUF ( void )
{
RXIFG = 0; // Clear interrupt flag
return RXBUF; // Read data from buffer
}
//----------------------------------------------------------------------
// ISR for Timer_A2 , channel 0: transmission
//----------------------------------------------------------------------
#pragma vector = TIMERA0_VECTOR
_ _interrupt void TIMERA0_ISR ( void ) // Acknowledged automatically
{
static uint8_t TXBitCount = 0; // Count bits transmitted
static uint16_t TXShiftReg; // Shift register for transmission
LED = 1; // Show start of activity
if (TXBitCount == 0)
{ // Ready to start new byte
if (TXIFG == 0)
{ // Byte available to transmit
TXShiftReg = TXBUF; // Load data from buffer
TXShiftReg |= BIT8; // Add stop bit after msb
TXIFG = 1; // Show that buffer is available
TXBitCount = 9; // Number of bits including stop bit
TACCR0 = TAR + BITTIME; // Delay until start of start bit
TACCTL0 = OUTMOD_5 | CCIE; // Clr output on compare for ST
}
else
{ // No data available , shut down
TACCTL0 = OUT | OUTMOD_0 | CCIFG; // Idle: output high ,
} // disable interrupt , set flag for int 'pt when reenabled
}
else
{ // Send next bit
if (TXShiftReg & BIT0)
{ // Send 1 next
TACCTL0 = OUTMOD_1 | CCIE; // Set output on compare
}
else
{ // Send 0 next
TACCTL0 = OUTMOD_5 | CCIE; // Clear output on compare
}
TACCR0 += BITTIME; // Delay until next bit
TXShiftReg >>= 1; // Shift right , remove lsb
--TXBitCount; // Update bit counter
}
LED = 0; // Show end of activity
}
//----------------------------------------------------------------------
// ISR for Timer_A2 , channel 1 and timer core ( inactive): reception
//----------------------------------------------------------------------
#pragma vector = TIMERA1_VECTOR
_ _interrupt void TIMERA1_ISR ( void ) // NOT acknowledged automatically
{
static uint8_t RXBitCount = 0; // Count bits received
static uint8_t RXShiftReg; // Shift register for reception
LED = 1; // Show start of activity
TACCTL1_bit. CCIFG = 0; // Acknowledge interrupt , clear flag
if (TACCTL1_bit.CAP)
{ // Capture mode , start bit detected
TACCTL1_bit.CAP = 0; // Switch to sampling (compare ) mode
TACCR1 += HALFTIME; // Wait for half a bit time
RXBitCount = 9; // Bits to receive including ST, SP
}
else
{
switch (RXBitCount)
{
case 9: // Start bit
if (TACCTL1_bit. SCCI)
{ // Error: start bit should be low
TACCTL1_bit.CAP = 1; // Abandon reception
}
else
{ // Correct: proceed to receive data
TACCR1 += BITTIME; // Wait for complete bit time
--RXBitCount; // Update bit counter
}
break ;
case 0: // Stop bit
if (TACCTL1_bit. SCCI)
{ // Correct: stop bit should be high
RXBUF = RXShiftReg; // Store data into buffer
RXIFG = 1; // Raise flag to show new data
} // (discard byte if stop bit low)
TACCTL1_bit.CAP = 1; // Return to capture mode
break ;
default : // Data bit (lsb first), cases 1-8
RXShiftReg >>= 1; // Shift data , clear msb for new bit
if (TACCTL1_bit. SCCI)
{
RXShiftReg |= BIT7; // Set received bit if high
}
TACCR1 += BITTIME; // Wait for complete bit time
--RXBitCount; // Update bit counter
break ;
}
}
LED = 0; // Show end of activity
}
