How do I define an i2c device that has multiple addresses.

RE: How do I define an i2c device that has multiple addresses.

Kenneth — Mon, 01 Sep 2025 12:26:59 GMT

Hi Chris,

Looks like the driver may actually already support this?
https://github.com/nrfconnect/sdk-zephyr/blob/main/drivers/eeprom/eeprom_at2x.c#L236

/**
* @brief translate an offset to a device address / offset pair
*
* It allows to address several devices as a continuous memory region
* but also to address higher part of eeprom for chips
* with more than 2^(addr_width) adressable word.
*/
static uint16_t eeprom_at24_translate_offset(const struct device *dev,
off_t *offset)
{
const struct eeprom_at2x_config *config = dev->config;

const uint16_t addr_incr = *offset >> config->addr_width;
*offset &= BIT_MASK(config->addr_width);

return config->bus.i2c.addr + addr_incr;
}

Kenneth

RE: How do I define an i2c device that has multiple addresses.

chrisstv — Wed, 27 Aug 2025 13:34:32 GMT

Sorry, as per the previous suggestion, This shows how to specify two different devices on one bus.

I have a single device with 4 addresses.

Which means you have to address the one single eeprom at 4 different addresses (50, 51, 52, 53) each address can access 64K of the eeprom array, making a total of 256k.

Regards

Chris

RE: How do I define an i2c device that has multiple addresses.

Kazi Afroza Sultana — Wed, 27 Aug 2025 13:12:01 GMT

Hello Chris,

You can have a look this example sdk-zephyr/samples/sensor/sgp40_sht4x/boards/blackpill_f411ce.overlay at main · nrfconnect/sdk-zephyr · GitHub; which shows how to add multple slave under one bus.

RE: How do I define an i2c device that has multiple addresses.

chrisstv — Tue, 19 Aug 2025 14:04:06 GMT

Hi Kazi,

No unfortunately in that example they are actually defining 3 different size EEPROMs I guess their development kit has 3 different size devices on their PCB.

My issue is that the M24M02 is a 2 Mbit (256K) eeprom. Given eeproms have only 2 x 8 bit address bytes (16 bits) but to access 2 Mbit (256K) you need 18 bits of address. ST use a 2 bit field in the eeprom address register for the extra 2 bits required.

Which means you have to address the eeprom at 4 different addresses (50, 51, 52, 53) each address can access 64K of the eeprom array, making a total of 256k.

Regards

Chris

RE: How do I define an i2c device that has multiple addresses.

Kazi Afroza Sultana — Tue, 19 Aug 2025 13:41:25 GMT

Hello Chris,

'' So my question is how do I configure the overlay so that the driver can access 4 addresses depenedent of the memory address to be accessed?

Do I have to define 4 different devices?''

This sounds correct. Looks like zephyr x_nucleo_eeprma2 board has similar way of defining eeprom.

source: sdk-zephyr/boards/shields/x_nucleo_eeprma2/x_nucleo_eeprma2.overlay at v4.1.99-ncs1-snapshot1 · nrfconnect/sdk-zephyr · GitHub

However, you need to make sure with the vendor as M24M02 eeprom is not out product.

Thanks.

Kazi