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Undefined identifier -- i2c_speed
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allenhuffman

Joined: 17 Jun 2019
Posts: 537
Location: Des Moines, Iowa, USA

Posted: Sat Apr 22, 2023 8:29 am

Ttelmah wrote:

3 to 27, implies a huge rise in bus capacitance.
What are your pull-ups?. Assume this is a 3.3v system?.
Tc and Tr are specified as 120nSec max for a 1MHz I2C bus. This
gives a Rp(max) of Tr/(0.8473*Cb). So for a bus capacitance of 200pF,
this gives 708R. Now with 27 devices, 200pF, is going to be close to the
minimum possible capacitance. So to have any hope of working you need
to either clock slower, or drop the pull-ups to perhaps 700R.

The I2C signal goes to some kind of transceiver on the board then that turns it in to some differential signal that runs over Ethernet type cables. I think the only pure 3V or 5V I2C is on the board itself.

"I2C in protocol only" I guess.

I need to go back in version control in our multiplexer board and see if it ever had 1000000 set.
_________________
Allen C. Huffman, Sub-Etha Software (est. 1990) http://www.subethasoftware.com
Embedded C, Arduino, MSP430, ESP8266/32, BASIC Stamp and PIC24 programmer.
http://www.whywouldyouwanttodothat.com ?

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