Input impedance of BS2 I/O pins

agentile

Does anyone know what the impedance of the I/O pins are?· I am assuming a couple of mega-ohms.· And, does the impedance change with the change in pin status (pin used as input or output)?

thanks

AG

Newzed

I have seen no answers to your query, so I offer the following, which may be or not be correct.

Max output of any pin is .035 amp at 5 volts.· This calculates to be

Z = 5/.035 = 142.8 ohms impedance.· Make sense?

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Sid Weaver
Do you have a Stamp Tester?

http://hometown.aol.com/newzed/index.html
·

Tracy Allen

The input impedance and the input leakage current is very high, typical of a CMOS input. That is in the gigaohm range--1000 megaohms. For example, a 0.1 microfarad capacitor hooked up to an input pin and charge to 5 volts can hold that for a minute or more, if there is no external leakage path.

And yes indeed the impedance changes when the pin is made an output. It drops to the order of 100 ohms. The output is a mosfet drain, so the resistance is lower (~50 ohms) when the output is lightly loaded; then the V/I curve bends over to look more like a current source (~30 ma) at heavy loads. The SX chips in the multibank Stamps can source and sink more current than the PIC in the original Stamp.

edit, correction: I should have said, "The input impedance is _very high_ and the input leakage current is _very low_, typical of a CMOS input."

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Tracy Allen
www.emesystems.com

Post Edited (Tracy Allen) : 1/8/2005 9:39:13 PM GMT

agentile

Tracy,

·Thanks.· That's exactly what I needed.



AG