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I understand that it's a type of ROM, but is there more to it? How can it be used for?

Diogo Magalhães
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1 Answers1

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EEPROMS (Electrically Erasable Programmable Read-Only Memory) are a type of non-volatile memory (they maintain the info even when not powered. You can read more about EEPROMS on Wikipedia.

They are used by Pi HATS (Hardware Attached on Top) EEPROM. Per the Raspberry Pi Foundation's blog.

The EEPROM holds the board manufacturer information, GPIO setup and a thing called a ‘device tree‘ fragment – basically a description of the attached hardware that allows Linux to automatically load the required drivers.

They should not be used for anything but communicating with the HAT's EEPROM.

The blog post announcing HATs can be found here, and the HAT spec can be found here.

Steve Robillard
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    Using GPIO 0/1 on a Pi3 (ID_SD/ID_SC) is pretty much a no no because that bus is also used to control internal GPIO. On earlier Pi models the bus may be used as a normal I2C bus if a HAT isn't being used. – joan Jun 25 '16 at 16:47
  • @joan I have also read that the Pi3 has a port expander, and it seems reasonable that this would be I²C but the pins seem to be in input mode. Are you aware of any documentation of the use? – Milliways Jun 26 '16 at 06:32
  • @Milliways I vaguely remember reading a post where someone mentioned the model number and I do remember a post where someone had communicated with the device to switch one of the Pi3 LEDs. They had put up github code which I haven't tried. The posts were on the raspberrypi.org forums. I'll have a look later and post a link if I can find the information. – joan Jun 26 '16 at 07:54
  • @Milliways Have a look at https://www.raspberrypi.org/forums/viewtopic.php?f=72&t=139753 which shows (indirectly via a link) how to control the activity LED on the Pi3. The best search string seems to be "port expander pi3". – joan Jun 26 '16 at 09:23
  • Actually @joan You can use GPIO 0 & 1 with very little work. For proof of this look at the Official Dots board. – Ryan Walmsley Jun 28 '16 at 19:12
  • @RyanWalmsley On a Pi3? The last time I checked there was regular GPU traffic on the I2C bus 0. – joan Jun 28 '16 at 19:47
  • @RyanWalmsley The Official Dots board test script only tests for using these as inputs, not outputs – plasmo Dec 05 '22 at 03:49