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PENTIUM® PRO PROCESSOR AT 150, 166, 180, and 200 MHz
4.2.3.3.
Receiver Ringback Tolerance
Refer to Section 4.1.3.1 for a complete description of
the definitions and methodology for determining
receiver ringback tolerance.
4.2.4.
System-Based Calculation of Required
Input and Output Timings
Below are two sample calculations. The first
determines T
and T
CO-MAX
determines T
. These equations can be used
HOLD-MIN
for any system by replacing the assumptions listed
below, with the actual system constraints.
4.2.4.1.
Calculating Target T
T
-M
SU
IN
T
and T
can be calculated from the
CO-MAX
SU-MIN
Setup Time equation given earlier in Section 4.1.4:
≤ T
T
FLIGHT-MAX
PERIOD-MIN
+T
+T
CLK_SKEW-MAX
As an example, for two identical agents located on
opposite ends of a network with a flight time of
7.3 ns, and the other assumptions listed below, the
following calculations for T
done:
Assumptions:
•
T
15 ns
PERIOD-MIN
•
T
7.3 ns
FLIGHT-MAX
•
T
0.7 ns
CLK_SKEW-MAX
(0.2 ns
skew)
•
T
CLK_JITTER-MAX
phase error)
•
T
??
CO-MAX
time)
•
T
??
SU-MIN
time)
Calculation:
•
7.3 ≤ 15 − (T
CO-MAX
•
T
+T
CO-MAX
SU-MIN
54
, while the second
SU-MIN
-
, and
CO
MAX
− ( T
+T
CO-MAX
SU-MIN
)
CLK_JITTER-MAX
and T
can be
CO-MAX
SU-MIN
(66.6 MHz)
(given flight time)
(0.5ns for clk driver)
for
board
0.2 ns
(Clock
(Clock to output data
(Required input setup
+T
+0.7 +0.2)
SU-MIN
≤ 6.8 ns
The time remaining for T
CO-MAX
split ~60/40% (recommendation). Therefore, in this
example, T
would be 4.0 ns, and T
CO-MAX
2.8 ns.
NOTE
This a numerical example, and does not
necessarily apply to any particular device.
Off-end agents will have less distance to the farthest
receiver, and therefore will have shorter flight times.
T
values longer than the example above do not
CO
necessarily preclude high-frequency (e.g. 66.6 MHz)
operation, but will result in placement constraints for
the device, such as being required to be placed in the
middle of the daisy-chain bus.
4.2.5.
Calculating Target T
To calculate the longest possible minimum required
hold time target value, assume that T
fourth of T
, and use the hold time equation
CO-MAX
given earlier. Note that Clock Jitter is not a part of the
equation, since data is released by the driver and
must be held at the receiver relative to the same
clock edge:
≤ T
T
+T
HOLD-MIn
FLIGHT-MIN
Assumptions:
•
T
4.0 ns
CO-MAX
•
T
1.0 ns
CO-MIN
•
T
CLK_SKEW-MAX
receiver
•
T
0.1 ns
FLIGHT-MIN
•
T
??
HOLD-MIN
Calculation:
•
≤ 0.1 +1.0 − 0.7
T
HOLD-MIN
•
≤ 0.4 ns.
T
HOLD-MIN
NOTE
This a numerical example, and does not
necessarily apply to any particular device.
E
and T
can be
SU-MIN
SU-MIN
HOLD-MIN
is one
CO-MIN
− T
CO-MIN
CLK_SKEW-MAX
(Max clock to data
time)
(Assumed ¼ of max)
0.7 ns
(Driver to
skew)
(Min of 0.5" at
0.2 ns/inch)
(Minimum signal hold
time)
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