TI/Stellarus Definition of "Weak"

Aug 02, 2011 5 Replies

No way are those weak pull ups 110k!!!



I just put a pull up on the JTAG reset pin of a TI LM3S2533, because my JTAG wasn't working and my 10M-ohm input VOM was reading the pin as being as low as low could be. I'm down to using #32 magnet wire as mod wire, to fit the pins on the processor, and if I have to change that sucker it's going to be a pain and a half.



The data sheet says 50k to 110k. Lessee. Ohms law. Fluke 77 has 10M- ohm input impedance, a "weak pull up" resistor of 110k-ohm should make it read 33mV below 3.3V, right? So when I read 0.15V, then either the laws of physics are being violated, my meter breaks only when I measure those voltages, or the stinking data sheet lies!!!



Grr.


www.wescottdesign.com

You need to enable the pullups on some ARMs, also they are sometimes not available on analog or other "special" pins.

John Devereux

Are you sure the weak pullup hasn't been disabled by accident? (doesn't it also have weak pulldowns available too - maybe a typo?)

Regards, Martin Brown

They're supposed to be there coming out of reset (particularly on this pin), and I'm explicitly setting them later.

www.wescottdesign.com

Un bel giorno Tim Wescott digitò:

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[...] 1.1 JTAG pins do not have internal pull-ups enabled at power-on reset [...]
Fletto i muscoli e sono nel vuoto.

Or your chip's broken or somebody programmed the pin as an output and it's outputting a low.

Hope This Helps! Rich

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