8051 ADXL SPI interfacing

8051cspi

I am trying to interface a ADXL345 to 8051 – AT89C51RC2 through SPI interface.

I have used the below code taken from here:

 include "Init.h"

 define SS_ADXL P1_0;

 void SPI_interr_routine(void);

 char serial_data;

 char data_example;

 char data_save;

 char transmit_completed;


void main(void)
{

    // Insert code
    Hardware_init();
    transmit_completed = 0;
    data_example=0x55;
    data_save = 0;
    printf("\n\r1111111111111");
    SPCON |= 0x10; /* Master mode */
    P1_1=1; /* enable master */
    SPCON |= 0x82; /* Fclk Periph/128 */
    SPCON &= ~0x08; /* CPOL=0; transmit mode example */
    SPCON |= 0x04; /* CPHA=1; transmit mode example */
    IEN1 |= 0x04; /* enable spi interrupt */
    SPCON |= 0x40; /* run spi */
    P1_1 = 0;
    EA=1; /* enable interrupts */
    //while(1) /* endless */
    //{
        SS_ADXL = 0;
        SPDAT= (0x32 | 0x80); /* send an example data */ //
        while(!transmit_completed);/* wait end of transmition */
        transmit_completed = 0; /* clear software transfert flag */

        SPDAT=0x00; /* data is send to generate SCK signal */
        while(!transmit_completed);/* wait end of transmition */
        transmit_completed = 0; /* clear software transfert flag */
        data_save = serial_data; /* save receive data */
        SS_ADXL = 1;
    //}

    printf("\n\r%c data_save = " , data_save);
}


void it_SPI(void) __interrupt (9) 
{

   SPI_interr_routine();

   return;

}

void SPI_interr_routine(void)
{

    if((SPSTA & 0x80) == 1)
    {
        serial_data = SPDAT;
        transmit_completed=1;
    }

    return;
}

Hardware Connections :

I have used this logic level converter to connect the 8051 to ADXL345.

P1.1 (SS) pin of 8051 is unconnected and I am enabling it in software by setting P1.1 to 1.

The CS pin of ADXL345 is connected to a GPIO of 8051 and I am selecting the slave (ADXL345) by setting the GPIO pin to low before writing / reading and then setting it high.
I am using the inbuilt SPI module in 8051.

When I run the above code, the SPIF bit is not getting set.

please let me know if anything is wrong with the hardware connection or the code.

Thanks

Best Answer

The ADXL345 Datasheet Rev E page 15 states "the timing scheme follows clock polarity (CPOL) = 1 and clock phase (CPHA) = 1". Make absolutely sure none of the timing limitations are violated. This chip in particular must follow the minimum and maximum timings shown on page 17. A digital-storage oscilloscope (preferred) or logic analyzer may be very helpful for troubleshooting.

Related Solutions

Electronic – Serial Peripheral Interface

A few points. That Maxim article targets a specific type of spi device. Mainly ones that are write only. Notice only MOSI is shown, not MISO. Additionally, these devices are chained, so data is shifted from one device to the other, like a shift register. (One common use of SPI peripherals on a microcontroller is to use them to drive common shift registers.)

SPI does not require the master to receive data. A slave is not required to respond. You can even have read only SPI devices, where the Master just clocks in data from the Slave (Only uses MISO). You can even have a 3 wire variation where MOSI and MISO are tied together (half duplex only). It all depends on the type of spi device you are using. Additionally, SPI can do Full Duplex transfers, but not all devices support this. As Wikipedia states, most devices do half duplex, even when wired in 4-wire mode.

In that note, the SPI devices are write only.

As for the clock frequency question, there is no auto negotiation of clock speeds. This is decided while the master is being programmed. You have to account for it.

C Programming for 8051: SFR directions as arguments

Edit: I changed code example to answer your question much better

I never used that chip, but it looks like a 8 bit variant of the 8051, so I would make the following guess: your port are defined as "sfr". Usually your MCU header file contains definitions such as :

sfr P1=0x90;

As per your chip's datasheet on page 5, P1 is at address 0x90. So that means that you could write something like that:

unsigned char scroll(sbit pin);

int main(int argc,char** argv)
{
 sbit pinMap[3]={P0^6,P0^7,P1^0}; // P0.6, P0.7 and P1.0.
 char keyboardRows[3]; // Keyboard layout is: one row per byte.  Column are mapped on 0 to 2.
 int i;

 while(1)
 {
  for(i=0;i<3;++i)
  {
   scroll(pinMap[i]);
  }
 }

 return 0;
}

unsigned char scroll(sbit pin)
{
 unsigned char rowState;
 pin=1; // or HIGH.

 // Save your column state in rowState here.

 pin=0; // or LOW?

 return rowState;
}

Now, an you didn't say what kind of problem you were having. We need more information to help you out.

Is it software or could it be hardware? software
What kind of error are you getting? I'm still not sure other than it doesn't work
It doesn't compile? It is fine.
It doesn't do what you expect? I still don't know what you get vs. what you expect.
Is it a custom matrix? Yes and it works.
Is so, have you used pull up resistors to set a definite state when the buttons are not pressed? It's ok.
Have to put diode to prevent ghost keys to appear (when pressing many keys at once)? It's ok.

Edit: Ok, your compiler don't like sbit as parameter, so one may try this:

unsigned char scroll(unsigned char* port,unsigned char pin);

int main(int argc,char** argv)
{
 unsigned char* portAddr={&P0,&P1,&P2}; // Put whatever here.
 unsigned char pin[3]={0x40,0x80,0x01}; // P0.6, P0.7 and P1.0.
 char keyboardRows[3]; // Keyboard layout is: one row per byte.  Column are mapped on 0 to 2.
 int i;

 while(1)
 {
  for(i=0;i<3;++i)
  {
   scroll(portAddr[i],pinMap[i]);
  }
 }

 return 0;
}

unsigned char scroll(unsigned char* port,unsigned char pin)
{
 unsigned char rowState;
 *port|=pin; // Let the bus weak pull-up pull the bus up.

 // Save your column state in rowState here.

 *port&=~pin; // Drive low the output.

 return rowState;
}

If you really insist on using sbit and such things, you could make the declaration global such as this:

sbit RowPins[3]={P0^6,P0^7,P1^0};

unsigned char scroll(int rowIndex);

int main(int argc,char** argv)
{
 char keyboardRows[3]; // Keyboard layout is: one row per byte.  Column are mapped on 0 to 2.
 int i;

 while(1)
 {
  for(i=0;i<3;++i)
  {
   scroll(i);
  }
 }

 return 0;
}

unsigned char scroll(int rowIndex)
{
 RowPins[i]=HIGH;

 // Read stuff here and put in "column".

 RowPins[i]=LOW;

 return column;
}

Best Answer

Related Solutions

Electronic – Serial Peripheral Interface

C Programming for 8051: SFR directions as arguments

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