External EEPROM (24LC256) interface WITH 12F675

[swamy]

Hi All

I am trying to interface an external EEPROM(microchip's 24LC256) with 12F675 and using PCW ver3.14,PCM ver 3.091. unfortunately i am not able to read or write to the external memory. I would greatly appreciate any help or pointers.

thanks
swamy


parts of the code i used are as follows,

#use i2c(master,sda=PIN_A1,scl=PIN_A2,slow)

void write_eeprom_now(u16 address, u16 value)
{
u8 lbyte;
u8 hbyte;
u8 albyte;
u8 ahbyte;

lbyte = value;
hbyte = (value >> 8);

albyte = address;
ahbyte = address >> 8 ;

i2c_start();
i2c_write(0xa0);
i2c_write(ahbyte);
i2c_write(albyte);
i2c_write(lbyte);
i2c_write(hbyte);
i2c_stop();
// check if write is done by EEPROM
do { i2c_start(); }
while(i2c_write(0xa0));
i2c_stop();
}

u16 read_eeprom_now(u16 address)
{
u8 lbyte = 0;
u8 hbyte = 0;
u8 albyte;
u8 ahbyte;

albyte = address;
ahbyte = address >> 8;

i2c_start();
i2c_write(0xa0);
i2c_write(ahbyte);
i2c_write(albyte);
i2c_start();
i2c_write(0xa1);
lbyte=i2c_read(1);
hbyte=i2c_read(0);
i2c_stop();

return( (u16)hbyte << 8 + lbyte);
}
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This message was ported from CCS's old forum
Original Post ID: 13597

[Pete Smith]

:=Hi All
:=
:=I am trying to interface an external EEPROM(microchip's 24LC256) with 12F675 and using PCW ver3.14,PCM ver 3.091. unfortunately i am not able to read or write to the external memory. I would greatly appreciate any help or pointers.

First thing to do is check to see if you've got pullup resistors on the SDA and SCL lines. Something around 2.2k should do. Without these, nothing will happen!

Also, check that WP is left floating or pulled to Vss/Vcc.
Also, you're using 0xA0 as the main device address. Make sure A0,A1 and A2 on the 24L256 are pulled low.

I can't see anything wrong with your code, quickly scanning it.

HTH

Pete.
___________________________
This message was ported from CCS's old forum
Original Post ID: 13599

[PCM programmer]

:=Hi All
:=
:=I am trying to interface an external EEPROM(microchip's 24LC256) with 12F675 and using PCW ver3.14,PCM ver 3.091. unfortunately i am not able to read or write to the external memory. I would greatly appreciate any help or pointers.
:=
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Do everything Pete says, but you should also look at this post:
<a href="http://www.pic-c.com/forum/general/posts/10971.html" TARGET="_blank">http://www.pic-c.com/forum/general/posts/10971.html</a>
___________________________
This message was ported from CCS's old forum
Original Post ID: 13619