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SPI interfacing problem between two 16F877A

Thu, 13 Mar 2008 02:25:14 -0700

I am reading the ADC of the master controller and sending the data to the slave through SPI.

Master is sending the data accurately, but slave is receiving in this fashion

Master send = 179
Slave read = 179 210 218 51 46 124 168 254 232 201 179 ..........
This means that I receive the correct data after 8 or 9 bytes as you can see the pattern shown above. Another thing is that I am sending this data on hyper terminal.

My code for master and slave is given below.

Master Code:

CODE:

#include <16F877A.h>//
#fuses NOWDT,NOPROTECT,XT,NOLVP,PUT
#use delay(clock=4000000)
#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7)
float val=0;
int8 data=0;





#int_TIMER0

void pick_sample(void)
{
set_timer0(150);
set_adc_channel(0);
delay_us(10);
val = read_adc();
data = (int8)val;

}


void main()
{

setup_timer_0(RTCC_INTERNAL|RTCC_DIV_16);       
set_timer0(150);

enable_interrupts(int_rtcc);
enable_interrupts(global);

setup_adc_ports(all_analog);
setup_adc(adc_clock_internal);

setup_spi( SPI_MASTER | SPI_H_TO_L | SPI_XMIT_L_TO_H | SPI_CLK_DIV_16 );

while(1)
{

spi_write(data);
printf("\n\rdata = %u dataf = %f",data,val);

}
}
 

Slave code:

CODE:

                                                   
//SLAVE program

#include <16F877A.h>//
#fuses NOWDT,NOPROTECT,XT,NOLVP,PUT
#use delay(clock=4000000)
#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7)

int8 data=0;


void main()
{

setup_spi(SPI_SLAVE|SPI_H_TO_L|SPI_SS_DISABLED);



        output_high(PIN_C4);
    output_high (PIN_C5);
while(1)
        {
               
        if(SPI_DATA_IS_IN())
{
                data = spi_read();
                         
                output_b(data);
               
                output_toggle(PIN_D4);

                printf("\n\r data = %u",data);
}
}
}

Please help me in this regard.

Re: SPI interfacing problem between two 16F877A

Thu, 13 Mar 2008 02:57:01 -0700

i do not understand this..
you are sending one byte and on receiver side you are getting bytes like 8 or 9 bytes...

Re: SPI interfacing problem between two 16F877A

Fri, 14 Mar 2008 07:30:56 -0700

I am sending from master 179 continuously, while slave is receiving the correct byte after 8 or 9th byte.That is correct data received after every 8th or 9th byte.

Re: SPI interfacing problem between two 16F877A

Fri, 14 Mar 2008 21:41:22 -0700

can you explain me in the slave code what are you doing here? and why?

CODE:

output_b(data);
               
output_toggle(PIN_D4);

Re: SPI interfacing problem between two 16F877A

Sun, 16 Mar 2008 22:13:49 -0700

By toggling D4 I am just want to make sure that slave is receiving the data and I am sending this data on port B. I have attached LED's on Port B and I just want to see the data on portB as well.

Re: SPI interfacing problem between two 16F877A

Mon, 17 Mar 2008 13:38:08 -0700

try doing this way...
in slave controller setup SPI as..

CODE:

setup_spi(SPI_SLAVE|SPI_L_TO_H|SPI_SS_DISABLED);

i mean.. L->H data transition.. please do it the right way..

The thing is.. master put data on o/p pin on H->L transition and slave read on L->H transition, this ensures that data is transfered properly..

Thats the reason you are getting correct data after exact 8 bits.. Everything will be fine if you just understand the reason..

Make the changes and try again..

Re: SPI interfacing problem between two 16F877A

Thu, 10 Apr 2008 01:34:14 -0700

It is still not working properly. May be it is a synchronization problem. Does any one has a program which he has tried himself?

Can any one tell me that "if I donot use SPI_READ() function, but read the data from SSPBUF register", than how can I read SSPBUF in C??????

Re: SPI interfacing problem between two 16F877A

Mon, 14 Apr 2008 06:22:11 -0700

hello,

Maybe the 'master' is running (and sending data) faster than the slave (because it has few instructions). Therefore, the data in the slave PIC gets corrupted. If I were you I would put a delay in the master and test it again.

BTW: Why did you put in the slave code the
output_high(PIN_C4);
output_high (PIN_C5);

pin_c4 is ther SDI and and C5 is the SDO