DSP56F801 Motorola Inc, DSP56F801 Datasheet - Page 24

• Manufacturer Part Number: DSP56F801
• Description: 56F801 16-bit Hybrid Controller
• Manufacturer: Motorola Inc

is designed to have no external load capacitors present. As shown in
should be used.
The 56F80x components internally are modeled as a parallel resonant oscillator circuit to provide a
capacitive load on each of the oscillator pins (XTAL and EXTAL) of 10pF to 13pF over temperature and
process variations. Using a typical value of internal capacitance on these pins of 12pF and a value of 3pF
as a typical circuit board trace capacitance the parallel load capacitance presented to the crystal is 9pF as
determined by the following equation:
This is the value load capacitance that should be used when selecting a crystal and determining the actual
frequency of operation of the crystal oscillator circuit.
3.5.2
It is also possible to drive the internal oscillator with a ceramic resonator, assuming the overall system
design can tolerate the reduced signal integrity. In
shown. Refer to supplier’s recommendations when selecting a ceramic resonator and associated
components. The resonator and components should be mounted as close as possible to the EXTAL and
XTAL pins. The internal 56F80x oscillator circuitry is designed to have no external load capacitors
present. As shown in
24
Note:
(which contain an internal bypass capacitor to ground).
Ceramic Resonator
Freescale
Figure 3-7
CL =
recommends only two terminal ceramic resonators vs. three terminal resonators
Figure 3-7 External Crystal Oscillator Circuit
Figure 3-8 Connecting a Ceramic Resonator
EXTAL XTAL
EXTAL XTAL
CL1 * CL2
CL1 + CL2
no external load capacitors should be used.
R
f
c
R
f
c
z
z
56F801 Technical Data, Rev. 16
+ Cs =
Recommended Ceramic Resonator
Parameters:
R
f
c
Recommended External Crystal
Parameters:
R
f
z
c
= 8MHz (optimized for 8MHz)
z
= 8MHz (optimized for 8MHz)
= 1 to 3 MΩ
= 1 to 3 MΩ
12 * 12
12 + 12
Figure
3-8, a typical ceramic resonator circuit is
+ 3 = 6 + 3 = 9pF
Figure 3-8
no external load capacitors
Freescale Semiconductor