Hi,
eines der bekannten ICM7216-Chips mit externem Oszillator. Der
Der Chip stammt von Harris; im Harris-Datenblatt ist dazu folgendes zu lesen:
External Oscillator Enable - In this mode, the signal at EXT OSC INPUT is used as a timebase instead of the on-board crystal oscillator (built around the OSC INPUT, OSC OUTPUT inputs). This input can be used for an external stable temperature compensated crystal oscillator or for special measurements with any external source. The on-board crystal oscillator continues to work when the external oscillator is selected. This is necessary to avoid hang-up problems, and has no effect on the chip's functional operation.
[Absatz von mir, denn es geht um den folgenden Text.]If the onboard oscillator frequency is less than 1MHz or only the external oscillator is used, THE OSC INPUT MUST BE CONNECTED TO THE EXT OSC INPUT providing the timebase has enough voltage swing for OSC INPUT (See Electrical Specifications). If the external timebase is TTL level a pullup resistor must be used for OSC INPUT. The other way is to put a 22MW resistor between OSC INPUT and OSC OUTPUT and capacitively couple the EXT OSC INPUT to OSC INPUT. This will bias the OSC INPUT at its threshold and the drive voltage will need to be only 2VP-P. The external timebase frequency must be greater than 100kHz or the chip will reset itself to enable the on-board oscillator.
irgendeine Vorgabe daraus beachten, da ja
- die Frequenz > 1 MHz bzw. > 100 kHz ist und
Multiplexsteuerung kann ja nach wie vor der interne Oszillator genutzt werden.
Was meint Ihr Experten?
Reinhard