PLUS+1 Hardware > Controllers

12V external pull-up

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Tor:
Hi,

I got an answer from the hardware team and it's more or less what Marbek_Elektronik mentioned.

"There should only be one pullup in the system. So, when the external pullup is present, the pin config enabling the internal one should not be used.
If the internal pullup is enabled, the system software would simply invert the pin’s logic in the .DigIn element, that is something the application can do as well. It should use an inverter to generate a TRUE from the digital input when it is pulled low."

About long term issues:
"If there is only the external pullup, I don’t think this will have any negative long-term effects. Important is either the internal or an external pullup shall be enabled, but not both at the same time."

I hope that answers the question, if not, please let us know.

Marbek_Elektronik:
Thanks.
But what about the long term issue, if ther are 2 pullups? (We shouldn't do this, I know.)

He doesn't want to change software and he added an external resistor.

Does it damage the 5V regulator? I think no. But what say the developers?

Tor:
Hi again,

Yes, forgot about the small thing about NOT changing the software. I'm sorry about that, but I'm used to be able to change the software.

Anyway, here's the answer from the hardware developer:
Q: "The customer wants to connect an external pullup to 12V to an input of a MC050-010 where the internal pullup to 5V is enabled. Seems like the customer does not want to change the software to disable the internal pullup. Would that have any negative effect on the hardware?"

A: "There will be no negative effects for this.  The pin is rated for 36V continuously.  It really makes no difference if the internal pull up is enabled or not since there are internal protection diodes to 5V on the side of the 15k pullup resistor not tied to the pin.
There will be up to 2mA ((36V-5V)/15k) going into the 5V supply with 36V applied, but this was accounted for in the design."

I hope this clarify most of the questions. If not, get back to us.

Have a nice day.

spittet:
Hi Tor, that is the exact answer I was looking for.

Thank you!

Sam

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