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???
04/22/07 04:55
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 		 #137746 - Youd be better off with a pair of DIY oscillators
Responding to: ???'s previous message
I'd advise against that.

If you build your own oscillator, using a hex inverter pack, for example, you can have two frequencies produced.

If you tie a 1k0 between pins 13 and 12 and between 11 and 10 then you can use the inverter on pins 9 and 8 to buffer what comes from pin 10. The crystal goes between pins 13 and 10, and a cap on the order of 150 pf goes between pins 12 and 11. I've had good luck with this.

If you have to switch between two "live" oscillators and can't tolerate glitches or runt pulses, as would be the case if you need to switch frequenies under software control, there's a schematic which you can find at XILINX.COM by searching for "unrelated clocks". It's part of a 6-part Peter Alfke app-note. http://www.xilinx.com/xlnx/xweb...ountryID=1

RE


List of 31 messages in thread
TopicAuthorDate
two crystals            01/01/70 00:00      
   Crystal connections            01/01/70 00:00      
      wires very very short            01/01/70 00:00      
         Youd be better off with a pair of DIY oscillators            01/01/70 00:00      
            why not use a derivative with a PLL?            01/01/70 00:00      
               What's a PPL?            01/01/70 00:00      
                  Phase Locked Loop            01/01/70 00:00      
                     It's not a very general sort of PLL            01/01/70 00:00      
                        apples and oranges            01/01/70 00:00      
                           Consider why one would want that ...            01/01/70 00:00      
                        PLL lock timing            01/01/70 00:00      
                           support droids didn't notice that ...            01/01/70 00:00      
                              .. err make that "jibe" : -)            01/01/70 00:00      
                     Atmel MCU with PLL?            01/01/70 00:00      
                        sometimes two wants do not jive            01/01/70 00:00      
                        sadly atmel 8051 derivatives dont            01/01/70 00:00      
            Am I right Richard?            01/01/70 00:00      
               What I meant ...            01/01/70 00:00      
   Koosha, we need an answer            01/01/70 00:00      
      What is in my mind...            01/01/70 00:00      
         why a switch ? It will give you all kins of proble            01/01/70 00:00      
         Maybe use a jumper instead of a switch?            01/01/70 00:00      
            better, yes, as good as none no.            01/01/70 00:00      
            it's commonly used.            01/01/70 00:00      
               all the story!            01/01/70 00:00      
                  Capacitor size            01/01/70 00:00      
                  whare is the uC?            01/01/70 00:00      
                     The uC is in the ZIF socket            01/01/70 00:00      
                  not this type of switch, please            01/01/70 00:00      
                  consider ALL the components!            01/01/70 00:00      
   Thank you!            01/01/70 00:00      

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