NULL Convention Logic conveniently and straightforwardly
delivers all of the traditionally expected benefits
of asynchronous circuit design.
Ease of Design
NULL Convention Logic circuits are purely symbolically
determined in that circuit behavior depends
solely on the interconnections among the gates.
Delay insensitivity is inherent in the logic
itself. It does not depend on subtle and expensive
circuit constructs. Consequently an NCL circuit
is a complete and autonomous expression in and
of itself. It signals its own completion of
processing and also signals its readiness to
accept new input data, without any appeal to
an external expression or authority such as
a clock, delay line or controller. NCL circuits
can be fully expressed in high level languages
without regard for timing issues and compiled
to silicon in the same sense that high level
programs are compiled to machine instructions.
Lower Design Cost and Risk
The clock is eliminated with all its attendant
design complexities and risks including clock
skew. The system can be designed in parts and
then directly composed. There are no global
coordination issues as with synchronous systems.
Lower Power Consumption
Only portions of the system that are doing useful
work consume power. Integrating logic function
and registration in a single gate reduces the
power required for system control. There is
no spurious switching of transistors. The NULL
state is an inherent and automatic power idle
state. The clock driving power is eliminated.
NCL systems operate entirely in terms of synchronized
wave fronts of monotonic level transitions.
There are no pulses or edge triggering involved
in the circuit behavior. The asynchronous nature
of NULL Convention Logic circuits distributes
the demand for power.
Convenient Technology Migration
Because the logic is inherently delay insensitive
it is insensitive to the behavior properties
of the physical implementation. NULL Convention
Logic circuits are insensitive to changes in
implementation technology, to changes in scale,
and to propagation delay changes due to aging
or manufacturing variations eliminating portability
and evolvability issues.
Automatic Adaptation to Physical Properties
The delays of the various circuit elements change
differentially with the change in physical parameters
such as voltage, temperature, age, manufacturing
variations and different implementation environments.
Since the circuits are delay insensitive, they
will continue to operate correctly over a large
range of variation of these physical parameters.
All failure modes due to timing problems (race,
hazards, skew, etc.) are eliminated. NCL
provides advantages for design cost and risk,
reliability of circuit performance and evolvability
beyond the barriers of complexity and feature
size facing clocked Boolean logic.
Testing complexity is reduced in that stuck-at-1
faults halt the circuit. Only stuck-at-0 faults
need to be exercised with applied patterns.
Design time and risk as well as circuit testing
requirements are expected to be decreased because
of the elimination of the complexity of the
clock with its critical timing issues.
Speed of Operation
NULL Convention Logic circuits are speed competitive
even though they require two propagation cycles
per unit of processing. They will operate at
the full rate the logic and material allow and
when appropriate will take advantage of average
case propagation behavior. There are no margins
added onto worst case propagation delays as
with clocked circuits. Integration of the registration
in logic gates allows more finely grained pipelining
and consequently higher throughput rates than
convention clocked techniques.
value NULL Convention Logic preserves all the
advantages of traditional Boolean logic (two
values, simple gates, straightforward synthesis)
while, additionally, providing self determined,
locally autonomous, self synchronizing, delay
insensitive, and fault detecting behavior. Furthermore,
NCL is compatible with the existing fabrication
and design infrastructure and with existing
clocked systems allowing convenient low cost