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M0KHZ
Joined: 14 Feb 2008
Posts: 18
Location: Cumbria
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| Multiple EEPROMs on I2C Bus |
 Posted: Tue Oct 07, 2008 1:39 am |
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I have two EEPROMs on my I2C bus, the chip select lines are:
EEPROM A – A0 Low, A1 Low, A2 Low
EEPROM B – A0 High, A1 Low, A2 Low
I am able to write and read to EEPROM with:
write_eeprom(pointer,data);
data = read_eeprom(pointer);
My question is which EEPROM is being used (I’m guessing EEPROM A),
if so how do I communicate with EEPROM B?
I’ve been looking at 24512.c and have found no clues.
Kevin – M0KHZ |
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drdelphi
Joined: 22 Apr 2007
Posts: 22
Location: Romania
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| Posted: Tue Oct 07, 2008 2:27 am |
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read_eeprom and write_eeprom are reading/writing from/to pic's internal eeprom.
to use two 24512 eeproms, first make sure you connect them properly to the pic and between themselves. that is:
- tie together all their pins except pin 1
- pin 1 of the first eeprom should be tied to ground and pin 1 of the second eeprom to Vcc
- tie pins 2, 3, 4 and 7 to ground
- tie eeproms' clock to PIN_C3 and eeproms' data to PIN_C4 (eg. for pic18f252)
- pull the clock and data lines to vcc through 2k2 resistors
all these being set, you can use the following functions to read and write from both eeproms :
| Code: | #ifndef eeCLOCK
#define eeCLOCK PIN_C3
#define eeDATA PIN_C4
#endif
#use i2c(master, fast, sda = eeDATA, scl = eeCLOCK)
void init_ext_eeprom(void) {
output_float(eeCLOCK);
output_float(eeDATA);
}
/*
dev is 0 or 1 (device number)
address is 0 - 65535 for 24512 (512 / 8 = 65536)
returns 1 if write succeeded, 0 otherwise
*/
int write_ext_eeprom(char dev, unsigned int16 address, char data) {
short int status;
char cmd, i2c_timeout;
i2c_timeout = 0;
cmd = 0xa0;
cmd += dev << 1;
i2c_start();
i2c_write(cmd);
i2c_write(address >> 8);
i2c_write(address);
i2c_write(data);
i2c_stop();
i2c_start();
status = i2c_write(cmd);
while(status == 1) {
i2c_timeout++;
if (i2c_timeout > 100) return(0);
i2c_start();
status = i2c_write(cmd);
}
return(1);
delay_ms(10);
}
char read_ext_eeprom(char dev, unsigned int16 address) {
char data, cmd;
cmd = 0xa0;
cmd += dev << 1;
i2c_start();
i2c_write(cmd);
i2c_write(address >> 8);
i2c_write(address);
i2c_start();
i2c_write(cmd + 1);
data = i2c_read(0);
i2c_stop();
return(data);
} |
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MicroManiac
Joined: 21 Aug 2008
Posts: 34
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| Posted: Tue Oct 07, 2008 2:28 am |
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This function writes on the internal EEPROM of the microcontroller not the external ones.
In order to use the external ones, you need to write the I2C functions manually
i think you can find sample code in the code library
_________________
"Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius -- and a lot of courage -- to move in the opposite direction."
Albert Einstein |
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M0KHZ
Joined: 14 Feb 2008
Posts: 18
Location: Cumbria
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| Posted: Tue Oct 07, 2008 3:17 am |
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Thanks guys, as usual I was doing something stupid 
I've checked the schematic and all OK, tonight I'll modify the code and try again, I'll let you know how I get on.
Kevin |
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Guest
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| Posted: Tue Oct 07, 2008 12:31 pm |
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All working great
Thanks again guys
Kevin - M0KHZ |
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