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Intel
®
820E Chipset
R
140 Design Guide
Term Definition
Flight time Flight time is a timing equation term that includes the signal propagation delay, any
effects of the system on the T
CO
of the driver, plus any adjustments to the signal at
the receiver needed to guarantee the setup time of the receiver.
More precisely, flight time is defined as the time difference between a signal at the
input pin of a receiving agent crossing V
REF
(adjusted to meet the receiver
manufacturer’s conditions required for AC timing specifications; i.e., ringback,
etc.) and the output pin of the driving agent crossing V
REF
, if the driver was driving
the test load used to specify the driver’s AC timings.
The V
REF
guard band takes into account sources of noise that may affect the way an
AGTL+ signal becomes valid at the receiver. See the definition of the V
REF
guard
band.
Maximum and Minimum Flight Time. Flight time variations can be caused by
many different parameters. Obvious causes include variation of the board dielectric
constant, changes in the load condition, crosstalk, V
TT
noise, V
REF
noise, variation
of the termination resistance, and differences in I/O buffer performance as a
function of temperature, voltage, and the manufacturing process. Less obvious
causes include the effects of Simultaneous Switching Output (SSO) and packaging
effects.
Maximum Flight Time is the largest flight time a network will experience under
all variations of conditions. Maximum flight time is measured at the appropriate
V
REF
guard-band boundary.
Minimum Flight Time is the smallest flight time a network will experience under
all variations of conditions. Minimum flight time is measured at the appropriate
V
REF
guard-band boundary.
GTL+ GTL+, the bus technology used by the Pentium
®
Pro processor, is an incident wave
switching, open-drain bus with pull-up resistors that provide both the high logic
level and termination. It is an enhancement of GTL (Gunning Transceiver Logic)
technology.
Network Trace of a printed circuit board (PCB) that completes an electrical connection
between two or more components
Network length Distance between extreme bus agents on the network. It does not include the
distance of the connection between the end bus agents and the termination resistors.
Overdrive
region
Voltage range, at a receiver, located above and below V
REF
for signal integrity
analysis.
Overshoot Maximum voltage allowed for a signal at the processor core pad. See each
processor’s datasheet for the overshoot specification.
Pad A feature of a semiconductor die contained within an internal logic package used to
connect the die to the package bond wires. A pad is only observable in simulation.
Pin A feature of a logic package used to connect the package to an internal substrate
trace
Ringback Voltage that a signal rings back to after achieving its maximum absolute value.
Ringback may be due to reflections, driver oscillations, etc. See the respective
processor’s datasheet for the ringback specification.
Settling limit Defines the maximum amount of ringing at the receiving pin that a signal must
reach before its next transition. See the respective processor’s datasheet for the
settling limit specification.
Setup window Time between the beginning of Setup to Clock (T
SU_MIN
) and the arrival of a valid
clock edge. This window may differ for each type of bus agent in the system.