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GTL+ INTERFACE SPECIFICATIONS
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 necessarily preclude high-
CO
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.
8.2.4.2.
CALCULATING TARGET T
To calculate the longest possible minimum required hold time target value, assume that T
is one fourth of T
MIN
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
CO-MIN
Assumptions:
T
CO-MIN
T
CLK-SKEW-MAX
T
FLIGHT-MIN
CLK
ADJ
Calculation:
T
= 1.07 + 0.4 - 0.45 - 0.78
HOLD
T
= 0.24
HOLD
This a numerical example, and does not necessarily apply to any particular
device.
8.3.
PACKAGE SPECIFICATION
This information is also included for designers of components for a GTL+ bus. The
package that the I/O transceiver will be placed into must adhere to two critical parameters.
They are package trace length, (the electrical distance from the pin to the die), and package
capacitance. The specifications for package trace length and package capacitance are
specified in the Pentium II I/O buffer models available from Intel's website at
www.intel.com. Please see your Intel representative for more information.
8-20
NOTE
, and use the hold time equation given earlier. Note that Clock
CO-MAX
- T
FLIGHT-MIN
CLK-SKEW-MAX
1.07 ns
(Assumed ¼ of max)
0.45 ns
(Driver to receiver skew)
0.40 ns
(Min of 0.5" at 0.2 ns/inch)
0.78 ns
(Required adjustment for flight time)
NOTE
HOLD
- CLK
ADJ
CO-
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