Monday, 8 May 2017

spi - MCP4131 resistor on SDI/SDO multiplexed pin?


I'm using the MCP4131 digital potentiometer to control the brightness of a LED using an Arduino Uno. The MCP4131's interface is SPI and it has a multiplexed SDI/SDO pin (pin #3).



The datasheet specifies a resistor R1 to be placed on the host's SDO before the host SDI/SDO signal are being multiplexed. I was wondering how to calculate it's value? For now, I used a 1k resistor and it works but I want to learn how to deduce this value from the datasheet.


The comment says that R1 must be sized to ensure VIL and VIH of the devices are met, I can't figure out what these are.


If anyone can explain I'll appreciate it, thank!


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