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PIC16F737 wtih SPI External EEPROM

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jaqpot
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PIC16F737 wtih SPI External EEPROM

Posted: Fri Dec 29, 2006 6:17 am

Hi !

I try to write and read data with a external Eeprom from microchip using SPI hardware of my PIC 16F737, the external eeprom is 25AA256.
I didn't find any drivers for it but I found a drivers for a 25LC640 which are almost the same except memory size.

Here is my code : eeprom function, then main programm...

Code:

#include <16F737>
#fuses HS, NOWDT, NOPROTECT, BROWNOUT, PUT
#use delay(clock=16000000)
#use rs232(baud=114000, xmit=PIN_C6, rcv=PIN_C7)

#define SPI_MODE_0_0 0x4000
#define SPI_MODE_0_1 0x0000
#define SPI_MODE_1_0 0x0010
#define SPI_MODE_1_1 0x4010

#ifndef EEPROM_SELECT
#define EEPROM_SELECT PIN_A5
#define EEPROM_CLK PIN_C3
#define EEPROM_DI PIN_C5
#define EEPROM_DO PIN_C4
#endif

#define EEPROM_ADDRESS long int
#define EEPROM_SIZE 32768

void init_ext_eeprom()
{
output_high(PIN_B6);
output_high(EEPROM_SELECT);
setup_spi(SPI_MASTER | SPI_MODE_0_0 | SPI_CLK_DIV_64 );
}

//--------------------------------
int1 ext_eeprom_ready(void)
{
int8 data;

output_low(EEPROM_SELECT);
spi_write(0x05);
data = spi_read(0);
output_high(EEPROM_SELECT);
return(!bit_test(data, 0));
}

//--------------------------------
void write_ext_eeprom(EEPROM_ADDRESS address, BYTE data)
{
while(!ext_eeprom_ready());

output_low(EEPROM_SELECT);
spi_write(0x06);
output_high(EEPROM_SELECT);

output_low(EEPROM_SELECT);
spi_write(0x02);
spi_write(address >> 8);
spi_write(address);
spi_write(data);
output_high(EEPROM_SELECT);
}
//--------------------------------

BYTE read_ext_eeprom(EEPROM_ADDRESS address)
{
int8 data;

while(!ext_eeprom_ready());

output_low(EEPROM_SELECT);
spi_write(0x03);
spi_write(address >> 8);
spi_write(address);

data = spi_read(0);
output_high(EEPROM_SELECT);

return(data);
}

/*
// If your hardware SPI pins are different than the
// ones used on the 16F877, then define them here
// and un-comment this section.
#define EEPROM_SELECT PIN_A5
#define EEPROM_CLK PIN_C3
#define EEPROM_DI PIN_C5
#define EEPROM_DO PIN_C4
*/

#include <STDLIB>
//========================
void main()
{
int8 data;
int8 wrote;
int16 addr;
int16 errors = 0;

delay_ms(5000);

//set_tris_c(0b00000000);
init_ext_eeprom();

// Fill eeprom with random data.
printf("\n\r");
printf("writing");

srand(0x55);

for(addr = 0; addr < EEPROM_SIZE; addr++)
{
write_ext_eeprom(addr, (int8)rand());
if((int8)addr == 0)
putc('.');
}

// Read the eeprom and check for errors.
printf("\n\r");
printf("reading");

srand(0x55);

for(addr = 0; addr <EEPROM_SIZE>= 100)
break;
}

if((int8)addr == 0)
putc('.');
}

printf("\n\r");
printf("done\n\r");

while(1);
}

by executing this programm, nothing is written in the eeprom (the programm return 100 lines with "data = 0x00" ... I'm not sure about my setup_spi .. can anyone help me ?

ckielstra

Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

Posted: Fri Dec 29, 2006 8:04 am

Code:

for(addr = 0; addr <EEPROM_SIZE>= 100)
break;
}

When posting code, please select the checkbox for disabling HTML code, now the above code fragment is corrupted. Or, even better, become a member of this forum and you can edit messages you have already posted and you can disable the HTML setting by default in your profile settings.

Quote:

I'm not sure about my setup_spi

Your SPI-setup looks correct, that is, if your chip is similar to the 25LC640. I didn't look at the datasheets. However, instead of hardcoding the values for the different SPI-modes I would use the defines from the CCS include files. Doing so will reduce the risk of CCS changing values in a new compiler release.

Code:

#define SPI_MODE_0_0 (SPI_L_TO_H | SPI_XMIT_L_TO_H)
#define SPI_MODE_0_1 (SPI_L_TO_H)
#define SPI_MODE_1_0 (SPI_H_TO_L)
#define SPI_MODE_1_1 (SPI_H_TO_L | SPI_XMIT_L_TO_H)

One problem in your program is that you didn't disable the analog ports. In the PIC processors many pins have multiple possible uses, for example pin A5 can be a digital input, output, slave select input, analog input or comparator 2 output. By default the analog pins get priority over the digital input/output functions, so you will have to disable all other port functionality by adding the following lines to the start of your program.

Code:

setup_adc_ports(NO_ANALOGS);
setup_comparator(NC_NC_NC_NC);

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