A couple electrical questions

cde

Hi collection of human beings who follow this forum due to their interest in the chip known as Propeller I,

I have just received my Propeller Education Kit which by the way is great and really well done. I had a couple basic questions:

* What would happen if by mistake I had a pin tied to GND without a resistance, and then configured it as output and set it to 1? Would it fry just this pin, or the whole Propeller?

* Same question with a pin tied to VCC and outputting 0.

Mike Green

Theoretically, it would fry that I/O pin. It turns out that Beau did some testing of Prop 1 I/O pins under those circumstances and they seemed to be just fine after many minutes of such abuse. The Prop isn't guaranteed to behave that way, but it does show that the Prop is very well designed and tolerant to some kinds of abuse.

Don't plan to subject the Prop to supply voltages in excess of 4V though, make sure you put bypass / filter capacitors (like 0.1uF/100nF) across both pairs of Vdd/Vss pins, and make sure you have short, substantial connections between the Vdd pins and between the Vss pins.

cde

Mike Green wrote: »

Theoretically, it would fry that I/O pin. It turns out that Beau did some testing of Prop 1 I/O pins under those circumstances and they seemed to be just fine after many minutes of such abuse. The Prop isn't guaranteed to behave that way, but it does show that the Prop is very well designed and tolerant to some kinds of abuse.

Don't plan to subject the Prop to supply voltages in excess of 4V though, make sure you put bypass / filter capacitors (like 0.1uF/100nF) across both pairs of Vdd/Vss pins, and make sure you have short, substantial connections between the Vdd pins and between the Vss pins.

Thanks a lot for the fast reply Mike, the setup from the Education Kit indeed has two bypass capacitors (one per regulator), which I imagine is good practice. I'm unsure why there is a 5V regulator in addition to the 3.3V one, I guess later in the kit some devices will require 5V input -- also this would provide an additional level of protection in case of over/under voltage?

cde

Here is an interesting article about bypass capacitors:

http://www.seattlerobotics.org/encoder/jun97/basics.html