Hi,
Happy Holidays to everyone. :-)
I want to know which line of the code given below makes the program run in an infinite loop, i want to know exactly how the MCU is able to run the loaded program several times once we load the program, remove the debug-interface and power it up again.
The code example :
//******************************************************************************
// msp430x26x Demo - USCI_B0, SPI 3-Wire Master Incremented Data
//
// Description: SPI master talks to SPI slave using 3-wire mode. Incrementing
// data is sent by the master starting at 0x01. Received data is expected to
// be same as the previous transmission. USCI RX ISR is used to handle
// communication with the CPU, normally in LPM0. If high, P1.0 indicates
// valid data reception. Because all execution after LPM0 is in ISRs,
// initialization waits for DCO to stabilize against ACLK.
// ACLK = n/a, MCLK = SMCLK = DCO ~ 1048kHz. BRCLK = SMCLK/2
//
// Use with SPI Slave Data Echo code example. If slave is in debug mode, P1.1
// slave reset signal conflicts with slave's JTAG; to work around, use IAR's
// "Release JTAG on Go" on slave device. If breakpoints are set in
// slave RX ISR, master must stopped also to avoid overrunning slave
// RXBUF.
//
// MSP430F261x/241x
// -----------------
// /|\| XIN|-
// | | |
// --|RST XOUT|-
// | |
// | P3.1|-> Data Out (UCB0SIMO)
// | |
// LED <-|P1.0 P3.2|<- Data In (UCB0SOMI)
// | |
// Slave reset <-|P1.1 P3.3|-> Serial Clock Out (UCB0CLK)
//
//
// B. Nisarga
// Texas Instruments Inc.
// September 2007
// Built with CCE Version: 3.2.0 and IAR Embedded Workbench Version: 3.42A
//******************************************************************************
#include <msp430x26x.h>
unsigned char MST_Data,SLV_Data;
void main(void)
{
volatile unsigned int i;
WDTCTL = WDTPW+WDTHOLD; // Stop watchdog timer
if (CALBC1_1MHZ ==0xFF || CALDCO_1MHZ == 0xFF)
{
while(1); // If calibration constants erased
// do not load, trap CPU!!
}
BCSCTL1 = CALBC1_1MHZ; // Set DCO
DCOCTL = CALDCO_1MHZ;
for(i=2100;i>0;i--); // Wait for DCO to stabilize.
P1OUT |= 0x02; // P1 setup for LED and slave reset
P1DIR |= 0x03; //
P3SEL |= 0x0E; // P3.3,2,1 option select
UCB0CTL0 |= UCMST+UCSYNC+UCCKPL+UCMSB; //3-pin, 8-bit SPI master
UCB0CTL1 |= UCSSEL_2; // SMCLK
UCB0BR0 = 0x02; // /2
UCB0BR1 = 0; //
UCB0CTL1 &= ~UCSWRST; // **Initialize USCI state machine**
IE2 |= UCB0RXIE; // Enable USCI_A0 RX interrupt
P1OUT &= ~0x02; // Now with SPI signals initialized,
P1OUT |= 0x02; // reset slave
for(i=50;i>0;i--); // Wait for slave to initialize
MST_Data = 0x001; // Initialize data values
SLV_Data = 0x000; //
UCB0TXBUF = MST_Data; // Transmit first character
_BIS_SR(LPM0_bits + GIE); // CPU off, enable interrupts
}
#pragma vector=USCIAB0RX_VECTOR
__interrupt void USCIA0RX_ISR (void)
{
volatile unsigned int i;
while (!(IFG2 & UCB0TXIFG)); // USCI_B0 TX buffer ready?
if (UCB0RXBUF==SLV_Data) // Test for correct character RX'd
P1OUT |= 0x01; // If correct, light LED
else
P1OUT &= ~0x01; // If incorrect, clear LED
MST_Data++; // Increment data
SLV_Data++;
UCB0TXBUF = MST_Data; // Send next value; "TX/RX of master happens here"
for(i=30;i>0;i--); // Add time between transmissions to
} // make sure slave can keep up
Please let me know the line, because of which the program runs again and again. Thanks.
