COP8SA-DM National Semiconductor, COP8SA-DM Datasheet - Page 177

• Manufacturer Part Number: COP8SA-DM
• Description: MODULE DEBUGGING FOR COP8SA
• Manufacturer: National Semiconductor

Specifications of COP8SA-DM

• Module/board Type: Debugger Module
• For Use With/related Products: Cop 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *COP8SA-DM

purpose of inductive decoupling is to force nodes internal to the processor, which are not
switching, into providing the charge for the nodes which are switching.
Ferrite beads are very effective for this type of decoupling due to their lossy nature.
Rather than storing the energy and returning it to the circuit later, ferrites will dissipate
the energy as a resistor.
One should be aware of potential repercussions from the use of any type of series
isolation from the power supply. Due to the reduced V
which may be present during
CC
switching transients, interfacing to other devices in the system may be a problem. Since
the V
should only be reduced for the duration of the switching transient, this should
CC
only be a problem if the other devices have especially sensitive and fast-responding
inputs.
2.23.5 Output Series Resistance
The addition of resistance in series with outputs can have a significant effect on the
emissions caused by the switching of the outputs.
Outputs that drive large capacitive loads can have a lot of current flowing when they
switch. While the series resistance may slow the switching speed of the node and thus
affect the propagation delay, it can also have a large effect on emissions by reducing the
amplitude of the current spike that charges or discharges the load.
2.23.6 Oscillator Control
One very definite source of emissions is the system clock. The oscillator is intended to
switch at high speed and therefore will emit some noise. Keeping the circuit loop of the
oscillator as small as possible will help considerably.
Ceramic resonators are available with the capacitive load included in a single three
terminal package. The use of these devices and placing them right next to the processor
can reduce emissions as much as 10 dB.
RC oscillators are particularly troublesome for emissions due to the high transient
current when the processor turns on the N-channel device that discharges the capacitor.
The transistor is meant to be large and to turn on strongly in order to discharge the
capacitor as quickly as possible. This allows simple control over the frequency of
oscillation but causes difficulty for the designer of systems for EMI-sensitive
applications.
2.23.7 Mechanical Shielding
A last resort for controlling emissions is the addition of mechanical shielding. While
shielding can be effective and can be easier from an electrical design standpoint, the
implementation and installation of a proper electromagnetic shield can be excessively
costly and time consuming.
It is much better to design the system with the control of emissions in mind from the start
rather than to apply bandages when it is time to begin production.
COP8SAx7 MICROCONTROLLER
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