Oscillator
cheap clonazepam paxil online real ringtones sildenafil online cheap soma ambien online wellbutrin online cheap adipex propecia online free real ringtones diethylpropion online free polyphonic ringtones cheap rivotril free jazz ringtones cheap lipitor lorazepam online cheap prozac order carisoprodol free polyphonic ringtones online tenuate cheap valium free polyphonic ringtones lipitor online free free ringtones phentermine online sagem ringtones free ringtones buy ultracet ortho online buy vigrx nexium buy meridia free sharp ringtones free music ringtones cheap diazepam cheap carisoprodol but wellbutrin meridia online free ringtones buy xanax free mtv ringtones order fioricet mp3 ringtones free nextel ringtones adipex online cheap xanax free sagem ringtones diazepam online clonazepam online polyphonic ringtones cheap carisoprodol buy wellbutrin free kyocera ringtones ativan online viagra online lorazepam online ultram online free kyocera ringtones cheap alprazolam free alltel ringtones ambien online vicodin online motorola ringtones free sony ericsson ringtones punk ringtones buy viagra but phentermine xanax online buy ultram cheap valium cingular ringtones adipex online cheap cyclobenzaprine cheap propecia tenuate online cheap carisoprodol ultracet online cheap pharmacy online wwe ringtones diazepam online xenical online nokia ringtones free qwest ringtones zanaflex online cheap diazepam free verizon ringtones free motorola ringtones order lortab prozac online free ericsson ringtones but ortho cyclobenzaprine online celexa online free free ringtones online phentermine cool ringtones cheap prozac qwest ringtones cialis online sprint ringtones cheap nexium free real ringtones sagem ringtones tracfone ringtones nokia ringtones punk ringtones free mp3 ringtones sony ringtones buy ativan cheap hgh free midi ringtones alltel ringtones cheap flexeril free sony ericsson ringtones motorola ringtones cheap vicodin tracfone ringtones soma online cheap levitra motorola ringtones cheap didrex cheap sildenafil cheap pharmacy online cheap zoloft order hydrocodone free sony ringtones cingular ringtones viagra buy paxil buy ambien lortab online hydrocodone online vigrx online cheap ativan hgh online sildenafil online buy viagra ortho online nextel ringtones online lisinopril funny ringtones sony ericsson ringtones buy vicodin cheap hydrocodone ativan online mono ringtones clonazepam online online levitra free sprint ringtones cialis online sony ringtones levitra online cheap zanaflex cheap phentermine celexa online ultracet online free wwe ringtones sharp ringtones buy norco soma online cheap ultracet free cingular ringtones adipex online cheap xenical albuterol online tenuate online ortho online free music ringtones sagem ringtones cheap lisinopril meridia online cheap propecia vigrx online cheap diethylpropion albuterol online mp3 ringtones cheap meridia free free ringtones cheap ultram soma online lortab online sildenafil online nextel ringtones lorazepam online funny ringtones diethylpropion online free free ringtones funny ringtones cingular ringtones cheap soma free nokia ringtones clonazepam online zyban online clomid online prozac online valium lisinopril online cheap meridia tramadol online free sharp ringtones The vast majority of electronic systems operate at some fixed frequency.
Usually the component that fixes that frequency is a crystal made of silicon, sealed in a metal can. (Some very-low-cost devices might use a "resonator" or a resistor and a capacitor to fix the frequency).
The entire circuit that generates the frequency is called an "oscillator". (An oscillator that uses a resistor and a capacitor to fix the frequency is called a "RC oscillator". An oscillator that uses a crystal to fix the frequency is called a "crystal oscillator".)
The oscillator includes, in addition to the frequency-fixing component just mentioned, an amplifier and capacitors.
One can buy an "oscillator" in a metal can. Typically an oscillator can has 4 pins. Inside the can is all the components of the oscillator. One applies DC power on 2 of the pins, and the oscillating signal (the "CLK OUT") appears on another pin. (The remaining pin is unused).
Other times one buys just the crystal in a (2-pin) metal can and attaches the other components to build an oscillator.
In either case, the frequency is printed on the top of the metal can.
Many microcontrollers have 2 pins (typically labeled "XTAL1" and "XTAL2", or "OSC1" and "OSC2", or something similar) that are designed to be directly connected to the 2 pins of a crystal. (Capacitors from those pins to VCC and GND are also part of the recommended circuit). An inverter inside the microcontroller acts as the amplifier, and the crystal and capacitors make up the rest of the oscillator.
In systems with multiple CPUs, it is often simpler, cheaper, and more reliable (avoiding metastability problems) to use a single crystal (rather than a dedicated crystal for each CPU). CPUs (and many other components) often have a single "CLK" pin designed to be connected to the wire used to send that "clock signal" (a fixed frequency) everywhere.
Unfortunately, many people confuse the "clock signal" generated by an oscillator (a simple metronome beat, tone, at constant frequency) with far more complicated "clock system"s that keep track of seconds, minutes, hours, and sometimes days, weeks, months, and years.
