Specifications

PENTIUM® PRO PROCESSOR AT 150, 166, 180, and 200 MHz E
54
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
CO-MAX
and T
SU-MIN
, while the second
determines T
HOLD-MIN
. These equations can be used
for any system by replacing the assumptions listed
below, with the actual system constraints.
4.2.4.1. Calculating Target T
CO
-
MAX
, and
T
SU
-M
IN
T
CO-MAX
and T
SU-MIN
can be calculated from the
Setup Time equation given earlier in Section 4.1.4:
T
FLIGHT-MAX
≤ T
PERIOD-MIN
− ( T
CO-MAX
+T
SU-MIN
+T
CLK_SKEW-MAX
+T
CLK_JITTER-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
CO-MAX
and T
SU-MIN
can be
done:
Assumptions:
• T
PERIOD-MIN
15 ns (66.6 MHz)
• T
FLIGHT-MAX
7.3 ns (given flight time)
• T
CLK_SKEW-MAX
0.7 ns (0.5ns for clk driver)
(0.2 ns for board
skew)
• T
CLK_JITTER-MAX
0.2 ns (Clock
phase error)
• T
CO-MAX
?? (Clock to output data
time)
• T
SU-MIN
?? (Required input setup
time)
Calculation:
• 7.3 ≤ 15 − (T
CO-MAX
+T
SU-MIN
+0.7 +0.2)
• T
CO-MAX
+T
SU-MIN
≤ 6.8 ns
The time remaining for T
CO-MAX
and T
SU-MIN
can be
split ~60/40% (recommendation). Therefore, in this
example, T
CO-MAX
would be 4.0 ns, and T
SU-MIN
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
CO
values longer than the example above do not
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
HOLD-MIN
To calculate the longest possible minimum required
hold time target value, assume that T
CO-MIN
is one
fourth of T
CO-MAX
, and use the hold time equation
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
HOLD-MIn
≤ T
FLIGHT-MIN
+T
CO-MIN
− T
CLK_SKEW-MAX
Assumptions:
• T
CO-MAX
4.0 ns (Max clock to data
time)
• T
CO-MIN
1.0 ns (Assumed ¼ of max)
• T
CLK_SKEW-MAX
0.7 ns (Driver to
receiver
skew)
• T
FLIGHT-MIN
0.1 ns (Min of 0.5” at
0.2 ns/inch)
• T
HOLD-MIN
?? (Minimum signal hold
time)
Calculation:
• T
HOLD-MIN
≤ 0.1 +1.0 − 0.7
• T
HOLD-MIN
≤ 0.4 ns.
NOTE
This a numerical example, and does not
necessarily apply to any particular device.