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2.1.1 Replacing the Clock Generator
When replacing the clock generator (U1), all you need to know is that there are two supply
levels. A 5V supply is available at Pin 14 and a 3.3V supply is available at Pin 11. To replace
it, just pop it out of the socket. Figure 2-2 illustrates that a 5V oscillator (with 3.3V output
only) can be used with a 14-pin form-factor, while 3.3V oscillators can be used with an 8-pin
form-factor.
Inserting a 14-pin form-factor 3.3V clock generator into U1 could cause permanent damage
to your device. Since the MPC821 clock input is not 5V-tolerant, any clock generator
inserted into U1 must have a 3.3V-compatible output. If you insert a 5V output clock
generator into U1, you could cause permanent damage to the MPC821 microprocessor.
MOTOROLA
14
1
7
GND
U1
Figure 2-2. U1 Power Sources
MPC821FADS-DB USER'S MANUAL
5V
3.3V
8
Installation
2-3
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