Specifications

4 DSP56800 Hardware Interface Techniques 
System Functions
2.2.2 External Clock Source
The recommended method of connecting an external clock is given in Figure 3. The external clock
source is connected to XTAL and the EXTAL pin is grounded.
Figure 3. Connecting an External Clock Signal using XTAL
It is possible to instead drive EXTAL with an external clock, though this is not the recommended
method. If you elect to drive EXTAL with an external clock source, the following conditions must be
met:
1. XTAL must be completely unloaded
2. The maximum frequency of the applied clock must be less than 8MHz
Figure 4 illustrates how to connect an external clock circuit with a external clock source using
EXTAL as the input.
Figure 4. Connecting an External Clock Signal using EXTAL
2.3 Power Management
The DSP56F80x power requirement depends on several factors, including mode of operation
(ACTIVE, STOP or WAIT), and system-level parameters including supply voltage, clock frequency,
operating temperature and output loading. Careful consideration of each of these factors can result in a
supply current requirement significantly less that the maximum found in the device Electrical
Specification. In the following sub-sections, plots are shown that apply only to the DSP56F805. These
are intended to show behavior of the device current requirement and do not supersede the device
Electrical Specification.
2.3.1 Device Model
The DSP56800 total current requirement (Itotal) is given by:
I
total
= I
digital
+ I
analog
I
digital
is given by:
I
digital
= C*V
DD
*f
DSP56F805
XTAL
EXTAL
External
GND
Clock
DSP56F805
XTAL
EXTAL
No
External
Connection Clock ( < 8MHz)
Frees
cale Semiconductor,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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