Lockup using xtal1 + pll16x

Comments

• cgracey Posts: 14,133

  2006-07-25 07:56 edited 2006-07-25 07:56

  That is odd. Either something is misconfigured or the chip is bad. Have you set the _xinfreq constant to the frequency of the crystal? Some demo programs rely on an accurate time constant. Can you use just XTAL1 without the +PLL16X? I ask the last question because I'm wondering if the crystal oscillator is functional independently of the PLL.
  

  glentech said...
  Using the blinkled.spin or any other program everything works unless I try to use the xtal1 + pll16x.

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  Chip Gracey
  Parallax, Inc.
• Beau Schwabe Posts: 6,547

  2006-07-25 15:32 edited 2006-07-25 15:32

  glentech,
  
  Just for kicks.... Does your "solderless breadboard" have a metal back or ground plane that could be introducing too much capacitance to the crystal and pins?
  
  XTAL1 has about a 36pF capacitance and is designed to handle a crystal range from 4MHz to 16MHz ... if the solderless breadboard is introducing a large amount
  of capacitance to the crystal, it might not oscillate properly or at all. XTAL2 has a lower capacitance (26pF) and XTAL3 has the lowest (16pF). Try using one of the
  other settings XTAL2 or XTAL3 on your solderless breadboard and let us know what happens.
  
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  Beau Schwabe
  
  IC Layout Engineer
  Parallax, Inc.
  
• glentech Posts: 35

  2006-07-25 17:17 edited 2006-07-25 17:17

  Thanks so much for your responses. I am posting on behalf of my son who has no Internet connection. I will send him the responses and he may have some more input. He seemed rather frustrated last evening, just got a new "toy" and couldn't get it to work like he expected. His name is Erik. My field is computers, but never much into this type of electronics. Fascinating, though, maybe I'll get hooked on it, too.
  
  Regards,
  Chester
• glentech Posts: 35

  2006-07-25 22:18 edited 2006-07-25 22:18

  the xtal1 works by itself. xtal1, 2 and 3 work fine with pll8x 4x all but 16x. If the solderless breadboard is changing the capacitance would the crystal work on some settings and not others? Here is another odd thing. If I run a program such as blinkled using the xtal1+pll16x setting (_xinfreq 5000000) and don't put the crystal in it works. If I put the crystal in while running (I know I'm probably not supposed to do that) it almost immediately stops. This also happens with the 1.84320 crystal I have.
  
  -Erik
• cgracey Posts: 14,133

  2006-07-25 23:23 edited 2006-07-25 23:23

  Could you try putting a 1uF cap right across VDD and VSS? Also, do you have a solid 3.3V supply? Perhaps there's a power-supply issue, or maybe the chip's just bad. BTW, putting the crystal in while the part's running won't hurt anything, but it will cause sub-minimal glitches on the system clock that will cause the chip to crash. Reset will get you back.
  

  glentech said...
  the xtal1 works by itself. xtal1, 2 and 3 work fine with pll8x 4x all but 16x. If the solderless breadboard is changing the capacitance would the crystal work on some settings and not others? Here is another odd thing. If I run a program such as blinkled using the xtal1+pll16x setting (_xinfreq 5000000) and don't put the crystal in it works. If I put the crystal in while running (I know I'm probably not supposed to do that) it almost immediately stops. This also happens with the 1.84320 crystal I have.
  
  -Erik

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  Chip Gracey
  Parallax, Inc.
• glentech Posts: 35

  2006-07-25 23:55 edited 2006-07-25 23:55

  I guess I overlooked the having the proper size capacitor between vss and vdd as when it is right it works like a charm. Thanks for the capacitance idea anyway. Beats me why it works that way though there must be some sort of feedback to the board or crystal that changes with the pll setting.
  
  
  - Erik
• cgracey Posts: 14,133

  2006-07-26 01:00 edited 2006-07-26 01:00

  The capacitor helps the power supply get over the short-term humps in supplying adequate current to the Propeller so that the voltage does not droop and cause a brown-out reset. A .1uF might work fine, too, but 1uF is more conservative. The farther away your 3.3V regulator is from the Propeller, generally, the more cap is required at the chip. I'm glad that was the problem. I keep offering "maybe it's a bad chip" when people have wierd problems, but that hasn't been the case yet, thankfully.
  

  glentech said...
  I guess I overlooked the having the proper size capacitor between vss and vdd as when it is right it works like a charm. Thanks for the capacitance idea anyway. Beats me why it works that way though there must be some sort of feedback to the board or crystal that changes with the pll setting.
  
  
  - Erik

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  Chip Gracey
  Parallax, Inc.