SPI MSP430 example.

Do you know where I can find a SPI that use 16-bits?

thanks for all

SPI effectively is a bitstream. So there is no difference in sending two 8 bit values or one 16 bit value. The USCI is not suited for transfers with transfer sized that are not a multiple of 8, but that is a very uncommon case (all SPI slaves I know of are padding to a multiple of 8 bits).

In fact, with the double-buffering (you can write the next byte to TXBUF while the last is being transmitted), you cannot tell a difference between two 8 bit transfers or one 16 bit transfer when scoping the line.

The only thing to do is that if the transfers are meant to be 16 bit that you need to always send two bytes (and two dummy bytes to receive a 16 bit value) and combine the received two bytes to a single 16 bit value. That´s basic C.

However, there IS are MSPs with (up to) 16 bit SPI. The USI module has an SPI that is not double buffered but allows any number of bits from 1 to 16. However, you have to wait for one word to be sent before you can configur ethe next transfer. Which makes programming a slave a really time-critical thing and also prevents maximum throughput (the transfer inherently stops after one transfer and before starting the next, since you have to configure the USI between single transfers).

Hello....

I try to finish the communication betwen 2 MSP430 but I didn't understandy how to get the start bit...

In this code example I stay all the time in __interrupt void universal_serial_interface(void) and   if (i == 0xBB) I get the correct data...

I know that I'm in a loop inside the serial interrupt because J is every time diferrent!

Plz Some one could help me to understand how to create a interrupt to se the start bit!

(the master code send 0xBB)

// USI interrupt service routine

#pragma vector=USI_VECTOR

__interrupt void universal_serial_interface(void)

{

  i = USISRL & 0xFF;

  j++;

  if (i == 0xBB)

  {

      USISRL = 0x09;

      USICNT = 8;                           // re-load counter

  }

}

#include <msp430g2221.h>

char i = 0;

char j = 0;

void main(void)

{

  WDTCTL = WDTPW + WDTHOLD;             // Stop watchdog timer

  P1OUT =  0x10;                        // P1.4 set, else reset

  P1REN |= 0x10;                        // P1.4 pullup

  P1DIR = 0x01;                         // P1.0 output, else input

  USICTL0 |= USIPE7 + USIPE6 + USIPE5 + USIOE; // Port, SPI slave

  USICTL1 |= USIIE;                     // Counter interrupt, flag remains set

  USICTL0 &= ~USISWRST;                 // USI released for operation

  USISRL = P1IN;                        // init-load data

//  USISRL = 0x0C;                        // init-load data  

//  USICNT = 8;                           // init-load counter

  _BIS_SR(LPM0_bits + GIE);             // Enter LPM0 w/ interrupt

}

// USI interrupt service routine

#pragma vector=USI_VECTOR

__interrupt void universal_serial_interface(void)

{

  i = USISRL & 0xFF;

  if (i == 0x0E)

  {

      USISRL = 0x09;

      USICNT = 8;                           // re-load counter

  }

}

Raul Rosetto Mu��oz said:

I didn't understandy how to get the start bit.

The USI module does not have UART capabilities (the only thing that has a 'start bit'). And the 'start condition' is part of the I2C protocol, supported by the USI, but not related to SPI too.

So either you're in the wrong thread or you have completely mixed-up some things.