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HCMOS TTL Crystal Oscillators — Parallax Forums

HCMOS TTL Crystal Oscillators

DWinchellDWinchell Posts: 60
edited 2006-02-14 03:38 in General Discussion
Will HCMOS TTL Crystal Oscillators drive the SX OK ?? Not sure what HCMOS drive levels are. http://www.mouser.com/catalog/619/566.pdf·do these look like they would work ?? If they will work is anyone ·intrested in a group buy of 50MHZ, 75MHZ, 80MHZ & 90MHZ please email David@Winchell.com·need 25 people and/or units min.

Comments

  • TransistorToasterTransistorToaster Posts: 149
    edited 2006-02-13 22:24
    An external oscillator module will drive the SX with no problem. Just hook the oscillator output to the OSC1 input. One detail is that if you are using the SX key, then you must take precautions because the SX key generates a 12V programming voltage on pin OSC1. Either unplug the oscillator module when using the SX key or put some protection circuitry (resitors, zeners, etc....) .
  • PJMontyPJMonty Posts: 983
    edited 2006-02-14 03:38
    Transistortoaster,

    Actually you need to disconnect the TTL oscillator from the chip in order to program it anyway. It seems that most of those oscillator chips have diodes on their outputs which prevent the the SXKey from being able to generate the 12V porgramming voltage. I learned this the hard way when I designed a PCB (and had about 5 proto boards etched) that used the enable on the oscillator to disconnect it from the SX chip. I couldn't get the thing to program until Stephen Holland (Hollander?) mentioned the diode thing. A few cut traces and suddenly everything was working. The next rev of the PCB had a jumper that actually disconnected the clock physically.
      Thanks, PeterM
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