Reading a EEPROM Memory with a PIC16f877 via SPI

[Spiffy]

I'm trying to write and read in a EEprom mem. The program, in C, is sent in a pic 16F877 by using a Qikstart card. I ran the program an got the results by Hyperterminal. I've also checked the writing sequence with an logic Analyser. The writting sequence is fine but when i'm trying to read the data inside, the data on the sdo line isn't clocked and gives me FF (which is a default setting for a memory when there is nothing inside).

here's my program!!!


#include "16f877.h"
#include "stdlib.h"
#use delay (clock=4000000)
#use rs232 (baud=9600,xmit=pin_c6,rcv=pin_c7)
#bit CKE = 0x94.6
#bit SMP = 0x94.7
#bit CKP = 0x14.4
#byte SSPSTAT=0x94
#byte SSPCON=0x14


//D�claration des variables


char choix;
int data=0,yx;
long int i=0;


void ecriture (void);
void lecture (void);
void main (void)

{

set_tris_C(0x90); //configure les ports pour sortie et entree.
set_tris_A(0x00);
set_tris_E(0x04);

setup_spi(spi_master|spi_l_to_h|spi_clk_div_16);

CKE = 0; // donn�e VALIDE de front descendant � front descendant
CKP = 0; // La m�moire �chantillone sur front montant
SMP = 0; // �chantillonage au centre d'un cr�neau
while(1)
{


Printf("\n\r1 pour activer l'�criture ou 2 pour la lecture");
choix=getch();


if (choix=='1')

{
ecriture();
}

if (choix=='2')
{
lecture();
}
else
{
puts("\n\r Erreur");
}
}


}

void ecriture (void)
{

printf("\n\r SSPSTAT:%x",SSPSTAT);
printf("\n\r SSPSTAT:%x",SSPCON);
printf("\n\r appuyer sur UN chiffre:");
yx=getch();
printf("\n\rlecture:%d",yx);
getch();
delay_ms(45);

output_low(pin_a4); //On choisi la memoire
spi_write(0x06); //Write enable

spi_write(0x02); //on veut ecrire sur la memoire
spi_write(0x00);
spi_write(0x00); //On choisi l'adress
spi_write(yx); //On designe le data a envoyer
output_high(pin_a4); //On enleve la selection de memoire
delay_ms(200);
printf("\n\r ok!");

}

void lecture (void)

{
printf("\n\r SSPSTAT:%x",SSPSTAT);
printf("\n\r SSPSTAT:%x",SSPCON);



printf("\n\rReading...");
output_low(pin_a4);
spi_write(0x03);
spi_write(0x00);
spi_write(0x00);
delay_ms(23);

While(i<10)
{
data=spi_read();
printf("\n\rlecture: %lu %x",i,data);
i++;
}
output_high(pin_a4);

}

[neil]

Hello Spiffy!

I have noticed in your code you are using "data=spi_read();" to read the data out. The CCS function is a bit strange here and when your SPI device is supplying the clock, you need to write data at the same time! Very strange, but try "data=spi_read(0);" This may be the only problem. I have not looked very closely at the rest of your code though.

Regards,
Neil.

[Snoopy]

Salut Spiffy

Il manque des details au niveau de la lecture.
Regarde: ceci vient avec le compilateur. va voir l'exemple

SPI_READ()

Syntax: value = spi_read (data)
Parameters: data is optional and if included is an 8 bit int.
Returns: An 8 bit int


Function:
Return a value read by the SPI. If a value is passed to SPI_READ the data will be clocked out and the data received will be returned. If no data is ready, SPI_READ will wait for the data.

If this device supplies the clock then either do a SPI_WRITE(data) followed by a SPI_READ() or do a SPI_READ(data). These both do the same thing and will generate a clock. If there is no data to send just do a SPI_READ(0) to get the clock.

If the other device supplies the clock then either call SPI_READ() to wait for the clock and data or use SPI_DATA_IS_IN() to determine if data is ready.

Availability:
This function is only available on devices with SPI hardware.

Examples:
in_data = spi_read(out_data);

Eample Files:
ex_spi.c

[Guest]

J'ai omis ce qui?

J'ai pens� que j'ai expliqu� cela!

[neil]

sorry, the last message was mine. Should have logged on!

[snoopy]

BYTE read_ext_eeprom(9356_ADDRESS address)
{
BYTE data;

rotate_left(&address,1);
output_high(MAX_CS);
spi_write(0x18|(address&1));
spi_write(address);
data=spi_read(0);
output_low(MAX_CS);

return(data);
}