funny thing with the prop clock and trying to output a signal

science_geek

i am trying to drive a transistor so that i can output a signal that is 5v. when i use the internal clock it all works without a hitch, but when i try to use a 10mhz or a 5mhz crystal it does absolutely nothing i need 80 mhz and made changes to thecode accordingly to compensate for the clock change. if i switch back to the internal clock it all works again. i have bumped up the pauses to try and compensate for the change in clock· but that still leads to nothing happening. im basically trying to pull one pin high and pulse another pin with a pwm

Mike Green

You may have blown your PLL. There's a known failure mode where the PLL selector stops working and the Propeller will only run off the internal clock. This failure occurs when there's poor power supply filtering and either not all power pins are connected or there are ground (or supply loops) where out of range voltages are induced in the Propeller chip. It can occur when there's reverse EMF from a relay or other coil switched by a transistor or by the Propeller itself without a protective diode across the coil.

Rayman

If you have these lines set right:

CON
_clkmode = xtal1 + pll16x
_xinfreq =5_000_000

then you probably did blow the PLL...

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science_geek

i have not hooked this prop up to a coil though, unless you can get back emf from a motor controller, and im using a computer power supply could that be the problem. is there any sure way to find out.

Sapieha

Hi science_geek.

What Board You use.
It is one of Parallax orginal else Homemade Board ?

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Sapieha

Mike Green

You can get noise on the power line (and/or ground) from the motor itself. It could be your computer power supply. How are you powering the Propeller?

The Propeller is pretty robust, but is sensitive to voltage spikes on the power supply. Not connecting all of the Vss and Vdd pins together or scrimping on bypass capacitors seems to be a good way to run afoul of this failure mode.

Post Edited (Mike Green) : 5/4/2009 4:20:17 AM GMT