MSP430FG4618 SPI can't receive data

Shang Wu

Intellectual 310 points

Other Parts Discussed in Thread: MSP430FG4618, ADC128S102

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Hi,

I’m using MSP430FG4618 (USCI port B) to drive ADC121S102. (MSP430FG4618/2013 Experimenter's board)

http://cache.national.com/ds/DC/ADC128S102.pdf

I was able to drive the ADC correctly (measured the output with an oscilloscope), but the received data always shows 00.

The following is a portion of my code. Can someone tell me where the problem is?
Thanks.

sync = 0;                                           // ADC Sync (enable)
UCB0TXBUF = TXdata1;                // Load shift register for first byte
while(!(IFG2 & UCB0TXIFG));                // wait for TX1 to complete
RXdata1 = UCB0RXBUF;           // Read-in the 1st received byte
UCB0TXBUF=TXdata2;                         // Load shift register for 2nd byte
while(!(IFG2 & UCB0TXIFG));                // wait for TX2 to complete
RXdata2 = UCB0RXBUF;            // Read-in the 2nd received byte
sync = 1;               // Raise ADC sync (disable)

over 14 years ago

0 Shang Wu over 14 years ago

Intellectual 310 points

Here's my code. Can anyone point out where the problem is? Thanks.

// Driving ADC128S102 - to acquire CH6 MSP430FG4618
// The readout of the ADC (pin15) should be around 110010101110 ----- 3.963Volt
// while the measured voltage is 3.957V
//Header1 P2: Data
//Header1 P6: /Sync (nSS)
//Header1 P8: SCLK
//----------------------------------------------------------------------
#include <io430xG46x.h>                // Specific device
#include <intrinsics.h>                // Intrinsic functions
#include <stdint.h>                    // Integers of defined sizes
//#include "LCDutils2.h"                // TI exp board utility functions

#define nSS        P3OUT_bit.P3OUT_0    // Output pin for _SS (active low)
uint8_t RXdata1=0, TXdata1 = 0x30;        // Received and transmitted data,
uint8_t RXdata2=0, TXdata2 = 0x00;        // Received and transmitted data,

void main (void)
{
    volatile uint16_t i;            // Loop counter to stabilize FLL+
    WDTCTL = WDTPW | WDTHOLD;        // Stop watchdog timer
    FLL_CTL0 = DCOPLUS | XCAP14PF;    // FLL+ divider, 14pF load caps
    SCFQCTL = 91;                    // f_DCO = 2(91 + 1)f_ACLK = 6.03MHz (Default D=2)
    SCFI0 = FLLD_2 | FN_3;            // Multiply by 2, 2.2 - 17MHz range
          P2DIR |= 0x06;                         //Set P5.1 to output direction -- LED is connected to this pin
          P2OUT = 0;//~BIT2|~BIT1; //turn off LEDs

    do {                            // Wait until FLL has locked
        for (i = 0xFFFF; i > 0; --i) {
        }                             // Delay for FLL+ to lock
        IFG1_bit.OFIFG = 0;            // Attempt to clear osc fault flag
    } while (IFG1_bit.OFIFG != 0);    // Repeat if not yet clear
    P3OUT_bit.P3OUT_0 = 1;            // High for nSS inactive
    P3DIR_bit.P3DIR_0 = 1;            // Enable for nSS output
    P3SEL = BIT1 | BIT2 | BIT3;        // Route pins to USCI_B for SPI

    UCB0CTL0 = UCCKPL | UCMSB | UCMST | UCMODE_0 | UCSYNC;
    UCB0CTL1 = UCSSEL1 | UCSWRST;    // Clock from SMCLK; hold in reset
    UCB0BR1 = 0;                    // Upper byte of divider word
    UCB0BR0 = 60;                    // Clock = SMCLK / 60 = 100kHz
    UCB0STAT = UCLISTEN;            // Internal loopback
    UCB0CTL1 &= ~UCSWRST;            // Release from reset
//    IE2_bit.UCB0RXIE = 1;            // Enable interrupts on receive
// Basic Timer: hold, counter 2 from ACLK, period = 8 (cntr 1 not used)

        BTCTL = BT_fCLK2_ACLK | BT_fCLK2_DIV8;
    BTCNT2 = 0;                    // Clear counter
    BTCTL &= ~BTHOLD;                // Start basic timer
    IE2_bit.BTIE = 1;                // Enable basic timer interrupts
    for (;;) {                    // Transmissions triggered by BT
        __low_power_mode_3();        // LPM3 between interrupts
    }
}
//----------------------------------------------------------------------
// ISR for basic timer: check TXIFG, activate nSS, start new SPI transfr
//----------------------------------------------------------------------
#pragma vector = BASICTIMER_VECTOR
__interrupt void BASICTIMER_ISR (void)    // Acknowledged automatically
{
                nSS = 0;                            // Lower nSS (make active)
                UCB0TXBUF = TXdata1;            // Load shift register for first byte
                while(!(IFG2 & UCB0TXIFG));             //wait for register to empty
             RXdata1 = UCB0RXBUF;            // Store received data (first byte)
                UCB0TXBUF=TXdata2;                      //2nd byte
                while((UCB0STAT&BIT0));                  //wait for the transmission to be completed
             RXdata2 = UCB0RXBUF;            // Store received data (second byte)
                nSS = 1;                            //Raise sync (nSS)

                if (RXdata1==0x0A)        // If upper byte received (0x0A is a known value from scope)
                  P2OUT=P2OUT|BIT2;       // Turn on LED1
                if (RXdata2 >= 0x01)       // If lower byte received (as long as it receives non-zero value)
                  P2OUT=P2OUT|BIT1;       // Turn on LED2
}

0 Shang Wu over 14 years ago in reply to Shang Wu

Intellectual 310 points

Although not perfect, here the solution

           uint32_t ADC_data;            // Converted value of temperature
           nSS = 0;                            // Lower nSS (make active)
           UCB0TXBUF = TXdata1;            // Tx first byte
           while (!(IFG2 & UCB0RXIFG));//wait for the data to be loaded on receiving buffer
           RXdata1 = UCB0RXBUF;            // Store received data (first byte)
           UCB0TXBUF=TXdata2;                      //Tx 2nd byte
           while((UCB0STAT&BIT0));                  //wait for the transmission to be completed
           RXdata2 = UCB0RXBUF;            // Store received data (second byte)
           nSS = 1;                            //Raise sync (nSS)
           ADC_data=(RXdata1<<8)+RXdata2;          //Combine High and Low

The only problem is that there's a clock delay between the first byte and 2nd byte. Although it does not affect the function of ADC.

0 Jens-Michael Gross over 14 years ago

Guru 227245 points

Shang Wu said:
UCB0TXBUF = TXdata1;                // Load shift register for first byte
while(!(IFG2 & UCB0TXIFG));                // wait for TX1 to complete
RXdata1 = UCB0RXBUF;           // Read-in the 1st received byte

Here's the problem: The SPI registers are double-buffered.

Once you wrote the first byte to TXBUF, it is immediately moved to the output shift and TXIFG is set once more. that does NOT mean that the previous content of TXBUF has been sent yet. In this case, just the first bit is in the process of sending. But TXBUF is ready to receive the next byte.

As a result, nothing (maybe not even the first bit) has been received yet. But you read RXBUF right now. Which contains nothing at this point.
Even after teh second byte has been moved from TXBUF to the output and TXBUF is empty the second time, the first byte does not necessarily have to be received and arrived in RXBUF yet. Since the output is sent at one while the input is received at the other edge of the clock signal. So you're reading the same still empty RXBUF once more.

To be sure that something has arrived, use the RXIFG bit (clear it before starting) and to ensure that the last transfer is complete, eitehr too rely on the RXIFG bit (which will be set after the last bit has been sent) or check the busy status bit.

0 Shang Wu over 14 years ago in reply to Jens-Michael Gross

Intellectual 310 points

Yes, that makes sense.

Thank you.

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MSP430FG4618 SPI can't receive data