COP8SA-DM National Semiconductor, COP8SA-DM Datasheet - Page 29

• Manufacturer Part Number: COP8SA-DM
• Description: MODULE DEBUGGING FOR COP8SA
• Manufacturer: National Semiconductor

Specifications of COP8SA-DM

• Module/board Type: Debugger Module
• For Use With/related Products: Cop 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *COP8SA-DM

which is independent of power supply and temperature changes, low cost and usable at
any frequency. As compared with other oscillator circuits, this circuit is not disturbed
very much by connecting a scope probe at any point in the circuit, because it is a stable
circuit and has low impedance. This makes it easier to monitor the circuit without any
major disturbance. The Pierce oscillator has one disadvantage. The amplifier used in the
circuit must have high gain to compensate for gain losses in the circuitry surrounding
the crystal.
Figure 1-10 shows the classic phase shift oscillator found not only on the COP8SAx7 but
on most other microcontroller circuits. It is the simplest oscillator in terms of component
complexity.
The Pierce is a series resonant circuit. For oscillation to occur, two criteria must be met:
The amplifier (intergrated on-chip) provides the desired gain and the 180˚ phase shift.
The external C
resistor is used at lower frequencies (typically lower than 2.5 MHz) to introduce losses
around the loop and prevent the oscillator going into harmonic oscillation. The R
resistor is used to bias the amplifier for better and quicker oscillator start-up.
Inputs/Outputs
Inputs and Outputs allow the microcontroller to communicate with external devices.
Inputs
1. The loop gain must be greater than one.
2. The phase shift around the loop must be 360˚
1
and C
2
Figure 1-10 Phase Shift Oscillator
capacitors provide the additional 180˚ phase shift. The R
C
2
An outside device forces a microcontroller pin high or
low. The logic level is read by the microcontroller as a
single bit of incoming information.
PHASE SHIFT
CRYSTAL
+
R
(180 )
LOSS
2
AMPL.
GAIN A
-
MICROCONTROLLER BASICS
C
R
1
1
OUT
1-17
1
2