MCP23008 power on reset and default values

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uflynn
 
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MCP23008 power on reset and default values

Post by uflynn »

All,

I have a mcp23008 that I am using with my rasberry pi. I am hooking it to 5v from the pi, and I am able to use i2c connect, and everything works great in that I am able to set a pin to on/off. However, when the chip is powered on, it's output pins are at 1.1v by default, even though the spec sheet says the gpio is set to all 0s. I suspect the chip is not hitting the POR values for some reason, but I have not been able to figure it out. I unplugged the i2c wires to make sure that was not a problem, as well. The reset is tied to 5v like in the tutorial, and I am using the gnd/power pins from the rasberry pi header port. Any ideas/suggestions on what I am doing wrong are appreciated!

Thank you!

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adafruit_support_rick
 
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Re: MCP23008 power on reset and default values

Post by adafruit_support_rick »

1.1v is within the range of logic 0. However, you might try some pulldown resistors to get to a true 0v.

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uflynn
 
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Re: MCP23008 power on reset and default values

Post by uflynn »

Rick,

Thank you for the suggestion on using pull-down resistors to make the voltage go to zero. I have found out with this device is that it's better to use it as a sink to ground, as it does not drive enough current to turn on a triac for my current application. Using it as a sink has worked great, and I don't worry that the device does not initialize the ports to 0 after being turned on.

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