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I2C pull-ups on 18F14Q41 need WPU active?

 
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Woody



Joined: 11 Sep 2003
Posts: 83
Location: Warmenhuizen - NL

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I2C pull-ups on 18F14Q41 need WPU active?
PostPosted: Mon Sep 09, 2024 3:29 am     Reply with quote

I managed to forget to put two pull-ups on a prototype I'm working on. No immediate need to heat up the soldering iron, because for birdbrains like me the 18F14Q43 contains I2C pull-up circuitry. Good thing I did use the 'standard' pins for I2C and the distance the bus covers on this PCB is 35mm.

After browsing the forum I saw mentioned more than once that, to make this work, not only the RxxI2C registers need to be set but also the WPU register for the I2C ports.

As I see no difference in risetime (~120ns @10x current) when enabling / disabling WPU for these pins I am wondering if this is still a valid suggestion or maybe just not needed this particular chip?

And while I sort of know the answer but keeping in mind that I only have one I2C slave on a short bus and I meet its .3uS max rise/fall time, would you use the internal I2C pull-ups on a production board? Or just no, not ever?
Ttelmah



Joined: 11 Mar 2010
Posts: 19529

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PostPosted: Mon Sep 09, 2024 6:34 am     Reply with quote

On this chip the I2C PU settings, allow you to select to use the standard weak
pull-up _or_ the I2C pull-ups (only on pins with this available).
Because you have used the standard pins (hurrah), you can set these bits
and get 2* the standard current or 10* the standard current (or 5/20*
when fast mode is enabled) This is independent of the standard weak
pull-ups. If you selected to use the standard pull-ups, they would have to be
enabled.

On quite a few older chips it is the standard pull-ups that are actually used,
with the option to increase their current. On these the weak pull-ups have to
be enabled.

Does not apply to this chip.

Turning the default pullups on should make a tiny difference, but only
a few percent. possibly a couple of nSec, but no more.
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