SPI tricky question.

Hi,

let me try to learn how SPI works in the Launchpad + MSP430G2452. My code (I wanted to do this based on interrupts but I was not having any success so I have to try simpler for now) is the following:

#include <msp430g2452.h>
#include <intrinsics.h>
#include <stdint.h>

uint8_t RXdata;

void main (void) {
 uint8_t i;

 WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer
 // pin most energy saving configuration
 P1DIR = 0xFF; // All P1.x outputs, it saves energy MSP430x2xx Family User's Guide
 P1OUT = 0; // All P1.x reset
 P2DIR = 0xFF; // All P2.x outputs
 P2OUT = 0; // All P2.x reset

 // Pull resistors on unused pins// Enable SDI, SDO, SCLK, msb first, master, enable output, latch data
 USICTL0 = USIPE7 | USIPE6 | USIPE5 | USIMST | USIOE;
 // Write then read (CPHA = 1 -> CKPH = 0), SPI not I2C, enable interrupt
 USICTL1 = USIIE;
 // SCLK = SMCLK / 128, clock idles high (CPOL = CKPL = 1)
 USICKCTL = USIDIV_7 | USISSEL_2;
 // Release USI from reset
 USICTL0 &= ~USISWRST;

 // SPI transfer
 USISRL = 0x46; // this is a READ, a WRITE would be 06
 P1OUT |= 0x40; // CS from low to high
 USICNT = 8;
 for (i = 0xFFFF; i > 0; i--); // Delay
 while (!(USIIFG & USICTL1)); // Counter clear?
 // this second byte is only important when writing 

USISRL = 0x69; 
 USICNT = 8;
 for (i = 0xFFFF; i > 0; i--); // Delay
 while (!(USIIFG & USICTL1)); // Counter clear?

 P1OUT &= ~0x40; //CS from high to low
 RXdata = USISRL;

 // Enter LPM0 & configure to be able to leave it by interrupt
 _BIS_SR(LPM0_bits + GIE);
}

After trying to write some value to the slave's SPI register (same code as above but with opcode 06), when I try to read the destination register, I only obtain 00 in USISRL and I should obtain... 0x69.  :( Argh! I think I've configured all correctly! Below you can see a WRITE transaction as expected by the slave device, and a READ transaction.

My questions are:

1. Do you think I should employ USI16B in SPI? (16 bit transfers). Or I can success with a similar strategy to my current one? What do you think? :)
2. As you can see here, the slave is operating on SPI mode = 01 (CHPA = 1, CPOL = 0). This is NOT the most common one in SPI, as far as I know. Since the most common ones are MODE0 and MODE3. Are my thought and source code correct?
3. Finally... I'm working with the LAUNCHPAD and employing, as typical in MSP430, P1.7 to 1.5 for SPI, and P1.4 as Chip Select. My question is... since P1.6 is also employed for the LED in Launchpad... perhaps this is affecting in my SPI communication? Should I move explicitly a jumper or something to devote 1.6 to SPI or the LED does not affect?

Please let me know your opinion! :) It is my first week with MSP430 so please be benevolent :)