MSP4320F24 I2C Sample code

The USCIAB0RX_VECTOR and USCIAB0TX_VECTOR service different types of interrupts.

The USCIAB0TX_VECTOR handles only interrupt flags that indicate if a character has been transmitted or received. The USCIAB0RX_VECTOR handles only Start and stop conidtion flags (UCSTPIFG and UCSTTIFG). All in all TX and RX are both handled in the USCIAB0TX interrupt, while I2C state changes are handled in the USCIAB0RX interrupt.

From page 17-24 of the 2xx User's Guide. USCI_Ax and USCI_Bx share the same interrupt vectors. In I2C mode the state change interrupt flags UCSTTIFG, UCSTPIFG, UCIFG, UCALIFG from USCI_Bx and UCAxRXIFG from USCI_Ax are routed to one interrupt vector. [USCIAB0RX]

The I2C transmit and receive interrupt flags UCBxTXIFG and UCBxRXIFG from USCI_Bx and UCAxTXIFG from USCI_Ax share another interrupt vector. [USCIAB0TX]

Hi,

Thanks for your reply, now I can able to get interrupts properly in both of my master board and slave board. But slave is not sending any ack ad it is pulling both the SCL and SDA line low after the R/W bit. While looking the UCB1STAT register, BUS busy and SCL is held low bit is setting always, also in this case im gettin the TX interrupt continuously. Kindly verify my code and say anything else to be done.

　

#include "msp430x26x.h"

unsigned char cTxdata = 0x55;

volatile unsigned char TXByteCtr;

unsigned int uiCount;

void main(void)

{

WDTCTL = WDTPW + WDTHOLD; // Stop WDT

if (CALBC1_16MHZ ==0xFF || CALDCO_16MHZ == 0xFF)

{

for(;;); // calibrate the side handle

// seg A DCO constants

}

BCSCTL1 = CALBC1_16MHZ; // Set DCO

DCOCTL = CALDCO_16MHZ;

for(uiCount=100;uiCount>0;uiCount--) // Wait for DCO to stabilize.

; /* void */ // stabilize Time - around 1 uS

P5SEL |= 0x06; // Assign I2C pins to USCI_B0

UCB1CTL1 |= UCSWRST + UCTR; // Enable SW reset + transmit

UCB1CTL0 = UCMODE_3 + UCSYNC; // I2C Slave, synchronous mode

UCB1I2COA = 0x48; // Own Address is 048h

UCB1CTL1 &= ~UCSWRST; // Clear SW reset, resume operation

UCB1I2CIE |= UCSTPIE + UCSTTIE; // Enable STT and STP interrupt

UC1IE |= UCB1TXIE; // Enable TX interrupt

asm("EINT");//_BIS_SR(GIE); // Enable global interrupt

while (1)

{

__no_operation(); // Set breakpoint >>here<< and

} // read out the TXByteCtr counter

}

#pragma vector = USCIAB1TX_VECTOR

__interrupt void USCIAB1TX_ISR(void)

{

UCB1TXBUF = ++cTxdata;

}

#pragma vector = USCIAB1RX_VECTOR

__interrupt void USCIAB1RX_ISR(void)

{

UCB1STAT &= ~(UCSTPIFG + UCSTTIFG); // Clear interrupt flags

}

BrandonElliott said:

The USCIAB0TX_VECTOR handles only interrupt flags that indicate if a character has been transmitted or received. The USCIAB0RX_VECTOR handles only Start and stop conidtion flags (UCSTPIFG and UCSTTIFG).

Can you comment on why those vectors are called _TX and _RX even though they are no handling what they indicate? :-) I know this is just a theoretical discussion now, but it really bothers me why those vectors are not called for example USCIAB0TR_VECTOR (TR like in UCTR flag that stands for Transceiver/Receiver) and USCIAB0FCTL_VECTOR (FlowConTroL)?

I suppose there is a reason for what they are called that I just don't get right now.

Best Regards,

tml

tml said:

Can you comment on why those vectors are called _TX and _RX even though they are no handling what they indicate? :-)

For SPI and UART mode, they do. However, on I2C, there's either RX or TX, but never both at the same time. So someone thought it would be smart to put both on one vector while the other one handles the additional interrupt sources (which don't exist in SPI or UART mode at all)

On 5x family, all interrupts of an USCI module (A or B separate) are handled by the same RXTX vector.

tml said:

it really bothers me why those vectors are not called for example USCIAB0TR_VECTOR

Because this would add some more aliases to the same vectors that handle RX and TX for SPI and UART. People would surely start using both for different ISRs and wonder why they get linker errors.