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The Mule
01-25-2008, 12:51 AM
How should unused pins on the Propeller chip be dealt with?
Semiconductor data sheets typically specify whether they should be connected to VDD, VSS or left unconnected, but I cannot find this information in the Propeller data sheet or Manual.
I'm using the chip in a very noisy electrical environment driving high voltage DC solenoids (via MOSFET drivers) and am seeing from 1.0 to 2.4 volts of "noise" when scoping the unused (floating( pins. Connecting a .01uF capacitor from the pin to VSS stabilizes the voltage at .84V or so. I can't tell that leaving the pins floating is causing any problems, but I absolutely cannot afford to have malfunctions caused by stray voltage, etc.

I see several options:
a). Do nothing
b). Set the pins to either inputs or outputs in the software
(If set to outputs, should they be set HI or LO, or connected to VDD or VSS?)
c). Decouple capacitively to VSS

Thanks in advance!



Phil Pilgrim (PhiPi)
01-25-2008, 01:00 AM
The safest approach would be either to set them as outputs or connect them, through resistors, either to Vdd or to Vss. Although each pin is protected internally by diodes to Vdd and Vss, if an unconnected pin were allowed to float, it may drift into the input circuitry's linear region, which would increase power consumption.

In experimental setups, I don't ever bother with either approach. But in a product design, it's an issue that really should be dealt with.

-Phil