gistfile1.c

/***
 * MSP430G2231
 * SPI Example
 * Using MCP23S17
 *
 * Kerry D. Wong
 * http://www.kerrywong.com
 *
 * 3/2013
 *
 * This program reads the GPIO pin status
 * from MCP23S17
 */
#include <msp430.h>

#define CS BIT4	// Chip Select on P1.4
#define REG_ADDR_IODIRA 0x00
#define REG_ADDR_IODIRB 0x01
#define REG_ADDR_GPIOA 0x12
#define REG_ADDR_GPIOB 0x13

void P1_init() {
	P1OUT = CS;
	P1DIR = CS;
	P1OUT |= CS;
} // P1_init

void USI_init() {
	// Enable SCLK, Master mode, enable output and reset USI
	USICTL0 = USIPE5 + USIMST + USIOE + USISWRST;

	// Mode 0 requires CKPH=1, enable interrupt
	USICTL1 = USICKPH + USIIE;

	// SMCLK div 8 -> 921.6 kHz USI clock
	USICKCTL = USIDIV_3 + USISSEL_2;

	// Clear USI for use
	USICTL0 &= ~USISWRST;

	USICNT = 1; // clear 1st transmit due to errata USI5
	__delay_cycles(50); // finish clearing (minimum (n+1)*16 cycles)
	USICTL0 |= USIPE7 + USIPE6; // Enable SDI/SDO pins.
	USICTL1 &= ~USIIFG;
} // USI_init

unsigned int w = 0;
void main(void) {
	WDTCTL = WDTPW + WDTHOLD;
	P1_init();
	USI_init();

	P1OUT &= ~CS;

	//01000000
	//address pins A2 A1 A0 are 000
	USISRL = 0x40;
	USICNT = 8;
	while (!(USIIFG & USICTL1));

	//By default IOCON = 0
	//Write to IO direction register
	USISRL = REG_ADDR_IODIRA;
	USICNT = 8;
	while (!(USIIFG & USICTL1));

	//set all directions to INPUT (default is input)
	USISR = 0xFF;
	USICNT = USI16B + 16;
	while (!(USIIFG & USICTL1));

	P1OUT |= CS;

	for (;;) {
		P1OUT &= ~CS;

		//01000000
		//address pings A2 A1 A0 are 000, read
		USISRL = 0x41;
		USICNT = 8;
		while (!(USIIFG & USICTL1));

		//Write to Port A
		USISRL = REG_ADDR_GPIOA;
		USICNT = 8;
		while (!(USIIFG & USICTL1));

		//clock out 16 bits
		USISRL = 0;
		USICNT = 16;
		while (!(USIIFG & USICTL1));

		P1OUT |= CS;

		//w contains the bits read from MCP23S17
		w = USISR;

		__delay_cycles(100000l);
	}
}