Specifications

System Functions
 DSP56800 Hardware Interface Techniques 7
2.3.5 Variation with Respect to Output Loading
Output loading influences supply current requirement in a manner similar to that described by the
model given in Section 2.3.1. Output load current for a given output pin is the sum of DC and AC
currents. The DC current requirement is that imposed by connected devices, such as TTL inputs. The
AC component is essentially a time-averaged capacitor charging current, which is dependent on V
DD
,
capacitance and switching frequency. The capacitance in this case is the sum of DSP56800 output
buffer capacitance, input capacitances of connected CMOS or other devices, and trace and stray
capacitances.
2.3.6 Power Dissipation
Minimization of power dissipation of the DSP56800 device is a slightly different problem than that of
minimizing the device’s supply current requirement. The chief difference lies in the way the I/O pins
of the device are exercised. For example, when a DSP56800 digital I/O pin sinks current, the internal
energy generated must be dissipated as heat, although literally this does not affect the DSP56800’s
current requirement, because this current does not enter the device through its V
DD
pins.
The specification of power dissipation for a given DSP56800 device is given in the corresponding data
sheet.
2.4 Reset/Interrupt Interfaces
2.4.1 Sources of Reset
The following sources of reset are present in this example system:
• Power-On Reset (POR)
• External Reset
• Computer Operating Properly (COP) Reset
Figure 8 illustrates how these RESET sources are used within the chip.
Figure 8. Sources of RESET
Hardware RESET
COP RESET
CORE
COP
External
RESET IN
res ires
Delay
pulse shaper
Delay
pulse shaper
(active low)
(active low)
system reset
Power on
Reset
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cale Semiconductor,
I
Freescale Semiconductor, Inc.
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