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spi.c
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spi.c
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/* spi.c
* Written by Connor McKee and Michael Georgariou
* CPE 316 - Spring 2020
*
* For use with the MSP432.
* DAC functions for use with the MCP4921. */
#include "msp.h"
#include "spi.h"
/* SPI_init
* initializes SPI communication on the MSP432. */
void SPI_init(void) {
/* first reset the EUSCI */
EUSCI_B0 -> CTLW0 |= EUSCI_B_CTLW0_SWRST;
/* next, set bits to do the following:
* polarity as active low
* enable synchronous mode
* use the SMCLK as the clock source
* set the MSB first selector
* set as the master */
EUSCI_B0 -> CTLW0 |= EUSCI_B_CTLW0_SWRST
| EUSCI_B_CTLW0_CKPL
| EUSCI_B_CTLW0_SYNC
| EUSCI_B_CTLW0_UCSSEL_2
| EUSCI_B_CTLW0_MSB
| EUSCI_B_CTLW0_MST;
/* set the CS bit as an output */
CS_PORT -> SEL0 &= ~CS_BIT;
CS_PORT -> SEL1 &= ~CS_BIT;
CS_PORT -> DIR |= CS_BIT;
CS_PORT -> OUT |= CS_BIT;
/* set the appropriate SPI port bits to run in primary mode */
SPI_PORT -> SEL0 |= (CLK_BIT | MOSI_BIT);
SPI_PORT -> SEL1 &= ~(CLK_BIT | MOSI_BIT);
/* and set these as outputs */
SPI_PORT -> DIR |= (CLK_BIT | MOSI_BIT);
SPI_PORT -> OUT |= (CLK_BIT | MOSI_BIT);
/* clear reset */
EUSCI_B0 -> CTLW0 &= ~(EUSCI_B_CTLW0_SWRST);
return;
}
/* send_to_DAC
* For use with the MCP4921. Takes in a 12-bit number, sent as a digital
* input to the DAC. */
void send_to_DAC(uint16_t output) {
uint8_t low;
uint8_t high;
/* get the lower 8 bits of the input and store it in low */
low = output & 0x0F;
/* get the higher 8 bits and store it in high */
high = (output >> 8) & 0x0F;
/* to send a command to the DAC, the highest 4 bits should be:
* 0, BUF, ~GA, and ~SHDN. See header file for explanation for each bit */
high &= ~(EN_BIT | BUF_BIT);
high |= GAIN_BIT | SHDN_BIT;
/* reset the CS bit low */
CS_PORT -> OUT &= ~(CS_BIT);
/* wait until transmit buffer is empty */
while (!(EUSCI_B0 -> IFG & EUSCI_B_IFG_TXIFG));
/* transfer the high 8 bits to the DAC */
EUSCI_B0 -> TXBUF = high;
/* wait until transmit buffer is empty */
while (!(EUSCI_B0 -> IFG & EUSCI_B_IFG_TXIFG));
/* send the low 8 bits */
EUSCI_B0 -> TXBUF = low;
/* wait for transmit to complete */
while(!(EUSCI_B0 -> IFG & EUSCI_B_IFG_RXIFG));
/* set the CS bit high */
CS_PORT -> OUT |= CS_BIT;
return;
}