STPD01 and its I2C addresses

[fabr]

Hi all,

Hoping this is this right subsection to post the following question...

I'm reading the STPD01 datasheet and it states its available I2C addresses : 4, 5, 6, and 7.

Reading to general I2C documentation, it seems that these addresses are reserved to I2C HS-Mode. 

So, is STPD01 an HS-Mode controller or a regular (100kHz) device? 

Links:

- https://www.ti.com/content/dam/videos/external-videos/en-us/8/3816841626001/6241024036001.mp4/subassets/adcs-introduction-to-i2c-reserved-addresses-presentation.pdf

- https://i2cdevices.org/addresses

- https://en.wikipedia.org/wiki/I2C

- https://learn.adafruit.com/i2c-addresses/the-list

[Peter BENSCH]

Welcome @fabr, to the community!

The (8-bit) addresses 0x00...0x07 mentioned in the I2C specification (e.g. found on Wikipedia) refer to the complete  (8-bit) address, including the 4 MSB as well as bit 0 (R/W). However, the address range of the STPD01 is defined by the bits specified in the data sheet, section 7.12.2, where bit 2 and bit 1 can be freely chosen by setting the ADD1 and ADD0 pins to the corresponding level. Since bit 0 only determines the data direction from the host's perspective (Read/Write), only the upper 7 bits are simplistically called the "address," which for the STPD01 lies between 0x00...0x07 (7-bit), corresponding to the 8-bit address range 0x08...0x0f. As correctly identified by you, the STPD01 can therefore be addressed with the 7-bit addresses 4...7.

Regarding the links you mentioned:

• The information from TI refers exclusively to the device mentioned there
• https://i2cdevices.org is a private collection of I2C addresses of devices that the user apparently uses or has tested
• https://learn.adafruit.com/i2c-addresses/the-list is also just a list compiled by Adafruit for a few devices

Compiling a list of all available I2C devices would be rather pointless, as a look into the respective data sheet is sufficient to find this information.

Your last question refers to the HS mode: HS stands for High Speed, i.e. 3.4 MHz. However, the STPD01 can only operate at a maximum in Fast Mode (400 kHz) (see data sheet, table 6, parameter SCLf).

Does this answer your questions?

Regards
/Peter

[fabr]

Thanks for the complete reply, but I still have a doubt. Assuming the common convention "the upper 7 bits are simplistically called the "address" (used also in the Wiki article), if I properly interpret the following table (extracted from wiki), the 6-th line tells that addresses 0x4 to 0x7 are reserved for HS-controller code. As you stated, STPD01 doesn't support HS, so I still don't get why this chip stays in this range.

I know Wiki is not the source of truth, but as I previously linked, many relevant players state the exact same knowledge.

To be clear, I'm just trying to figure out if it is a suggestion or a strict rule, and maybe I'm misinterpreting something.

 

[Peter BENSCH]

Well, the STPD01 is not an HS-mode I2C device, but a Fast-mode slave device and supports clock rates up to 400kHz only.
The address range 4 to 7 stated in the data sheet refers to the device’s 7-bit slave address configuration via the ADD0/ADD1 pins and is valid for this device. Generic reserved-address tables describe the I2C protocol in general, but they do not supersede the device-specific addressing information given in the data sheet.

Please note that I2C is generally limited to local communication (originally designed by Philips for Inter-Integrated Circuit communication for e.g. TV or CD players), where rules established for consumer devices in the last millennium no longer necessarily apply.

Regards
/Peter