MC56F8323EVM Freescale Semiconductor, MC56F8323EVM Datasheet - Page 31

• Manufacturer Part Number: MC56F8323EVM
• Description: KIT EVALUATION FOR MC56F8323
• Manufacturer: Freescale Semiconductor
• Type: DSPr

Specifications of MC56F8323EVM

• Contents: Module and Misc Hardware
• Processor To Be Evaluated: MC56F8322 and MC56F8323
• Data Bus Width: 16 bit
• Interface Type: RS-232
• For Use With/related Products: MC56F8322, MC56F8323
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Note:
3.2.3
The recommended method of connecting an external clock is illustrated in
connected to XTAL and the EXTAL pin is grounded.
relatively low impedance driver, as the XTAL pin is actually the output pin of the oscillator (it has a very
weak driver).
3.3 Use of On-Chip Relaxation Oscillator
An internal relaxtion oscillator can supply the reference frequency when an external frequency source of
crystal is not used. During a boot or reset sequence, the relaxation oscillator is enabled by default, and the
PRECS bit in the PLLCR word is set to 0. If an external oscillator is connected, the relaxation oscillator
can be deselected instead by setting the PRECS bit in the PLLCR to 1. If a changeover between internal
and external oscillators is required at start up, internal device circuits compensate for any asynchronous
transitions between the two clock signals so that no glitches occur in the resulting master clock to the chip.
When changing clocks, the user must ensure that the clock source is not switched until the desired clock
is enabled and stable.
To compensate for variances in the device manufacturing process, the accuracy of the relaxation oscillator
can be incrementally adjusted to within + 0.1% of 8MHz by trimming an internal capacitor. Bits 0-9 of the
OSCTL (oscillator control) register allow the user to set in an additional offset (trim) to this preset value
Freescale Semiconductor
Preliminary
2 Terminal
CL1
The OCCS_COHL bit must be set to 0 when a crystal resonator is used. The reset condition on the
OCCS_COHL bit is 0. Please see the COHL bit in the Oscillator Control (OSCTL) register, discussed
in the 56F8300 Peripheral User Manual.
External Clock Source
EXTAL XTAL
R
z
Figure 3-3 Connecting an External Clock Signal
CL2
Figure 3-2 Connecting a Ceramic Resonator
Resonator Frequency = 4 - 8MHz (optimized for 8MHz)
External
XTAL
Clock
C1
3 Terminal
EXTAL XTAL
56F8323 Technical Data, Rev. 17
EXTAL
R
V
SS
z
C2
The external clock input must be generated using a
Note: When using an external clocking
source with this configuration, the
“CLKMODE” and COHL bits of the OSCTL
register should be set to 1.
Sample External Ceramic Resonator Parameters:
R
z
= 750 KΩ
CLKMODE = 0
Figure
3-3. The external clock source is
Use of On-Chip Relaxation Oscillator
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