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The zener does have a small amount of reverse leakage current, enough to bleed off any accumulated charge.

Sounds like there could be quite a slow transition time from high to low for say a switch contact wired to +5vdc?

Lefty
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Fortunately there isn't a lot of capacitance to bleed off. Figure worst case of 100pF for the diode and 10pF for the I/O pin, charged to 5V gives a charge storage of 0.55nC. Discharging through a 1uA reverse leakage current gives a total discharge time of 550us. That's not a very long time relative to pushbutton press/release times.
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Okay, I'm not as dumb as I thought, I just couldn't believe you were relying on the zener's reverse leakage to pull the pin down. How would a resistor to ground in parallel with the zener affect the zener's capability to protect the input?


Edit:

Ahh, I see the source of some of my confusion, Andy's schematic is not a representation of the way your protection circuitry is connected. That explains everything. Thanks for the link : http://www.ruggedcircuits.com/html/mb324p.html#IOPins.
« Last Edit: July 23, 2009, 04:18:03 pm by EmilyJane » Logged

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The above schematic is now corrected but I just can't fire my cousin for his drafting mistakes.  ;D ;D ;D
Circuit D, I believe, might need a 10K pulldown?
 8-) 8-) 8-)
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Nope, no pulldown required in Circuit D because of the zener diode discussion above.
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Sources of power for the Gator and Gator+

There are two sources of power for the Gator.
One is from the USB port and the other one is the external 8-15 VDC supply input.

Question #1. What happens if both supply inputs(USB & External) are connected at the same time?

Question #2. Is there any "backfeeding" of supplies if both are connected at the same time?

 8-) 8-) 8-)
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External power takes precedence over USB.

Backfeeding is prevented by design. Specifically, no more than 5 microamps of current can flow from one supply to the other.
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Yes, it uses a Serial1 object in addition to the Serial object to access the second hardware serial port, just like the Mega uses Serial1, Serial2, etc.

That support is not in the 0016 release of the Gator Arduino tools but will be in 0017

What is the ETD when the release 0017 will be available?
 8-) 8-) 8-)
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We're following the Arduino software releases so when 0017 comes out, our latest changes will also come out in the "GATOR version".
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Is there a way to access and use the serial port (USB/PC serial port 0) on the Gator/Gator+
without using a PC? My application calls for using two TTL serial hardware ports.
 smiley
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No, PD0/PD1 are hardwired to the USB port.

I suppose you *could* solder some wires onto the board for PD0 and PD1 and bring those out for your own use :-)
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I suppose you *could* solder some wires onto the board for PD0 and PD1 and bring those out for your own use  

What are Arduino digital pin number(s) that are assigned to
the Gator's Serial Port 0 (default USB port)  PD0 & PD1 pins?

I know that by soldering wires to these pins voids
my warranty on the Gator?

BTW ... Soldering two wires to the surface mount 324P
is not an easy task for those attemping to try it!

 8-) 8-) 8-)
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What are Arduino digital pin number(s) that are assigned to
the Gator's Serial Port 0 (default USB port)  PD0 & PD1 pins?
Since those are dedicated serial port pins they do not have Arduino digital pin numbers. You can always add them yourself by editing the hardware/cores/arduino/pins_arduino.c file.

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I know that by soldering wires to these pins voids
my warranty on the Gator?

Yes, those lines are not externally protected thus if you apply overvoltage or negative voltage from an outside wire then you run the risk of damaging the AVR or the FT232 device.

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BTW ... Soldering two wires to the surface mount 324P
is not an easy task for those attemping to try it!

It is probably easier to solder some thin wire (e.g., 30AWG) into one of the vias for those lines. This image shows two accessible locations for soldering to the TXD and RXD lines:
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