Post by thread:[SX] ready to cut the umbilical sx-key

In SX Microcontrollers, SX/B Compiler and SX-Key Tool, ShadowsSoldier wrote:Hi folks. I am ready to disconnect my Sx-Key and let my SX ride the 5.125 MHz crystal all by itself in my circuit. Problem is, I don't know exactly how to do this. I have the crystal and inverter (if necessary) on my benchtop and am ready to go. Do I first make the oscillator with the 74AC04 (I don't need any help for this step...) or can I drive the SX with the crystal by itself? Anyhow, if someone could kindly give me a step-by-step I would appreciate it. Thanks!

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, bean wrote:BebopALot, It depends how close to 5.125 MHz you need to be. The SX will probably work by just putting the xtal onto the OSC1 and OSC2 pins and using OSCXT1 or OSCXT2 on the device line. If not, you may need some capacitors on each side of the xtal to ground. That should be in the area of �100ppM of 5.125 MHz. Bean.

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, ShadowsSoldier wrote:Thanks Bean, so to clarify, its unnecessary to say make a Pierce oscillator and drive it that way?

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, bean wrote:Try putting caps on each side of the crystal to ground. Bean.

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, ShadowsSoldier wrote:Bean you comment on how to choose capacitor specs that fall in the area of +-100ppm of 5.125 MHz - lets use .1uf cap. What are the calculations to determine?

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, bean wrote:0.1uF are WAY too big. Try 10 pF to 100 pF. Different value caps will offset the crystal frequency. You would need a calibrated frequency counter to be able to know how much the caps are pulling the frequency. Try different OSCxxx settings on the device line too. Bean.

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, lawlopez wrote:.1 uf ??? if you are putting .1 uf to ground either side of the crystal you are doomed. something like 20 pf would be a better choice.

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, ShadowsSoldier wrote:Thanks Bean and Mr. LawLopez. Can I use any 20-100 pf caps lying around, or do I need special ones ordered from digikey or mouser.com for example?

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