This is from the GM manual.


CRANKSHAFT POSITION SENSOR
Circuit Description
The crankshaft position (CKP) sensor is a sensor designed to detect changes in a magnetic field. The control module supplies the CKP sensor a signal and ground circuits. Ignition voltage is supplied to the sensor by an independent circuit. The CKP sensor produces a magnetic field whenever the ignition is ON. The CKP sensor is mounted near a reluctor wheel that is attached to the crankshaft. When the crankshaft rotates, when the engine is cranking or running, the toothed reluctor wheel changes the magnetic field. The CKP sensor converts each change in the magnetic field into a PULSE. The number of teeth on the reluctor wheel determines how many pulses the CKP sensor detects per crankshaft rotation. The CKP sensor signal is used in order to determine the engine speed, the crankshaft position, and to detect misfire.


CAMSHAFT POSITION SENSOR
Circuit Description
The camshaft position (CMP) sensor is a sensor designed to detect changes in a magnetic field. The control module supplies the CMP sensor with signal and ground circuits. Ignition voltage is supplied to the CMP sensor by an independent circuit. The CMP sensor produces a magnetic field whenever the ignition is ON. The CMP sensor is mounted near a reluctor wheel that is attached to the distributor shaft. When the distributor shaft rotates, or when the engine is cranking or running, the reluctor wheel changes the magnetic field. The CMP sensor converts each change in the magnetic field into a PULSE. The number of teeth on the reluctor wheel determines how many pulses the CMP sensor detects per camshaft rotation. The control module uses the CMP sensor signal in order to calculate the correct timing for sequential fuel injection.