#include "msp430x20x3.h"     //Header for MSP430F2013, located at
                             //C:\Programme\IAR Embedded Workbench\430\inc


//Function prototypes
void spi_init(void);         //Initialization of SPI
void v_out(void);            //Set output voltage of the d/a-converter


//Main function
void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;  //Stop watchdog timer to avoid timeout reset
  spi_init();                //Initialize SPI
  v_out();                   //Set output voltage
}


//SPI initialising function
void spi_init(void)
{
  P1DIR |= BIT0;             //Configure P1.0 (=BIT0) as output: LED
  P1DIR |= BIT1;             //Configure P1.1 (=BIT1) as output: CS2 for a/d-converter AD7787
  P1DIR |= BIT2;             //Configure P1.2 (=BIT2) as output: CS3 for d/a-converter MAX5530
  
  P1OUT &= ~BIT0;            //Switch off the LED (low-level)
  P1OUT |= BIT1;             //Set P1.1 (=CS2) on high-level to disable the AD7787
  P1OUT |= BIT2;             //Set P1.2 (=CS3) on high-level to disable the MAX5530
  
  USICTL0 |= USISWRST;       //Software reset; stop USI
  USICTL0 |= USIPE7 + USIPE6 + USIPE5 + USIMST + USIOE;
                             //Write to USI Control Register 0:
                             //  Activate ports P1.7 (MISO), P1.6 (MOSI), P1.5 (SCLK) for SPI
                             //  USIMST: USI Master Select; If bit is set (as here), then MSP430 is master
                             //  USIOE: USI Output Enable
  USICTL0 &= ~USILSB;        //Delete USILSB-bit to use MSB-first-mode

  USICKCTL = USISSEL_2 + USIDIV_2;   // SPI clock rate: SCLK = SMCLK /4
  USICTL0 &= ~USISWRST;      //USI released for operation: Delete "Software reset"-bit
  USICNT = 16;               //Load USI Bit Counter Register (Family user's guide chapter 10.2):
                             // USICNTx-Bits value: 16; in order to send 16 bit of data (16-Bit-converter)
                             // all other bits of this register are deleted
                             // USIIFGCC is one of these bits. Therefore USIIFG is set, if USICNTx reach zero
  USICNT |= USI16B;          //Set USI16B-bit of USICNT-register: enable 16-bit-shift-register mode in order
                             // to send 16 bit of data. So USISRL and USISRH shift registeres are used
                             // other bits are not modified
}

void v_out(void)
{
  int voltage;
  voltage = 0x0800;          //Set output voltage: 0800hex = 2048dec = 1.25 V
  P1OUT &= ~BIT2;            //Enable MAX5530 (set CS3 on low-level)
  USISR = 0xF000 + voltage;  //Control bits: 1111bin = Fhex; input data: voltage
  P1OUT |= BIT2;             //Disable MAX5530 (set CS3 on high-level)
}