i2c pullup resistors strictly needed?

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ljyang
 
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i2c pullup resistors strictly needed?

Post by ljyang »

So I'm laying out a circuit for an atmega328 and a mcp23017, which is an i2c port expander. If it is just the two components and then downstream (from the port expander) connections, are pullups strictly needed on the i2c lines? Nothing else on the i2c bus except the 328 and the mcp23017. Does the 328 have internal pullups on the i2c bus pins? I'm asking because I just send off a board design for prototypes and had a doh forehead slap moment when I noticed I'd left off the 4k7 pullups on the i2c bus. I'll greenwire up some pullups if they're absolutly needed for these prototypes, but was just wondering if the i2c comms would work well enough without them on there. I've already added them to the schematic and reworked the layout and will be sending off for another set of prototypes, but was just curious.

Thanks.

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adafruit_support_bill
 
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Re: i2c pullup resistors strictly needed?

Post by adafruit_support_bill »

The internal pullups are a much higher resistance and won't work well at high speeds.

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ljyang
 
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Re: i2c pullup resistors strictly needed?

Post by ljyang »

Cool. Thanks. I'll stop by the show and tell and show it off after the prototypes are done up

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