could this situation kill my chip

Lee Marshall

referring to all cmos micros:
when a pin is switched to an input, i assume a tristate buffer connecting the pin to an output d-latch is switched to high impedance, so
the contents of the output reg cannot conflict with incoming signals.
this is really a general question regarding electronics.
what would happen if 3.3v were applied to a pin that WAS in output mode and the latch contained a 0.(i am unfamiliar with the impedance characteristics of cmos) would something short and burn out, or would there just be a signal of 1.65v(in the middle) or something?

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The Propeller is the best micro!

srry if im sound a little unprofessional sometimes, im 15.

Post Edited (Mr Crowley) : 8/3/2007 7:37:40 AM GMT

Mike Green

It depends on how much current the 3.3V supply was capable of delivering. The output transistors are generally designed to handle currents on the order of 15-20ma with a usual maximum rating of 30ma (check the specific microprocessor's datasheet for specifics). If the 3.3V supply can deliver more than this amount of current, you will damage or literally melt either the connections involved on the chip or the output transistor itself depending on the amount of current involved. The Propeller's I/O pins can handle 40ma absolute maximum for example. The chip can probably withstand more than that, but is not guaranteed to do so.

Post Edited (Mike Green) : 8/3/2007 4:29:39 PM GMT

Lee Marshall

so would that mean i should put a 100ohm+ resistor at all inputs, incase this occurs when interfacing with another device.
also, on startup, what are the default pin directions?

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The Propeller is the best micro!

srry if im sound a little unprofessional sometimes, im 15.

Mike Green

The default direction for most microprocessors (and specifically Parallax's) is input mode.

For an example, the Stamp HomeWork Board has 220 ohm resistors in series with all the I/O pins to protect against this sort of accident. It's a risk reduction thing. The more sure you are of your circuit and your programming skills and care, the more you may be willing to do without the protective resistor. In some circumstances, the series resistor can interfere with what you're trying to do with the I/O pin.

Lee Marshall

thanks, mike, youve helped me a lot.
i think im gonna go write a guide for getting started with the propeller.

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The Propeller is the best micro!

srry if im sound a little unprofessional sometimes, im 15.

Paul Baker

BTW the Propeller is one of the rare microcontrollers that can handle a I/O short, we certainly dont recommend doing so, but I have personally done so in testing the chip for an extended period of time without burning it out (doing the same with a Basic Stamp or SX chip will result in the I/O pin quickly burning out).

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Mightor

Paul Baker (Parallax) said...
BTW the Propeller is one of the rare microcontrollers that can handle a I/O short, we certainly dont recommend doing so, but I have personally done so in testing the chip for an extended period of time without burning it out (doing the same with a Basic Stamp or SX chip will result in the I/O pin quickly burning out).

Is there anything the Prop *can't* do? [noparse]:)[/noparse]

I bet Prop V2 will solve world hunger and establish world peace. I just hope they get it finished on time. No pressure on the design team.

Gr,
Mightor

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