Electronics > Microcontrollers

UID STM32 and MAC address

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S. Petrukhin:
Hello, friends!

Tell me, please, does someone know the order of UID allocation in STM32? Which bits of 96 are the least significant and are they unique?

I want to use the UID part to set the MAC address of the device.
There is a desire to buy a MA-M block of 1M addresses in IEEE and I will need 20 unique bits.

Or should I not register my own OUI at all, use a locally administered MAC address with unique 46 bits?

JOEBOBSICLE:
Buy off the shelf chips with preprogrammed Mac addresses. They're cheap as chips and save a lot of hassle. Normally they have an i2c interface. Those 96 bits are only unique when compared against another 96 bits

S. Petrukhin:

--- Quote from: JOEBOBSICLE on May 16, 2021, 09:01:41 am ---Buy off the shelf chips with preprogrammed Mac addresses. They're cheap as chips and save a lot of hassle. Normally they have an i2c interface.

--- End quote ---

What kind of chips are you talking about?

nudge:
I use EUI-48 I2C EEPROMs from Microchip and they work well: https://www.microchip.com/en-us/products/memory/serial-eeprom/mac-address-and-unique-id-eeproms

technix:
If your product has volume, it may be economically viable to use your own MAC block. If so, You can use whatever mathematical method you find appropriate to condense the whole 96 bits into 20 bits. One idea would be using the onboard CRC hardware to generate a CRC32 from the UID, then use the lowest x bits from it.

If it is a small-run product, you should use some EEPROM with preprogrammed MAC address in it - 24AA025E48, 25AA256E48, etc. Those chips have a permanently locked sector holding the preprogrammed MAC address, while the rest of the chip is useable as a standard I2C or SPI EEPROM holding configuration data.

p.s. Octavo Systems, can you guys replace the 24AA32 in your SiP products with 24AA025E48 in the future? Having a MAC address preprogrammed would be very useful, and all your products have Ethernet support.

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