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2.4
Reserved, Unused, and TESTHI Signals
All RESERVED lands must remain unconnected. Connection of these lands to V
V
, or to any other signal (including each other) can result in component malfunction
TT
or incompatibility with future processors. See
processor and the location of all RESERVED lands.
In a system level design, on-die termination has been included by the processor to
allow signals to be terminated within the processor silicon. Most unused GTL+ inputs
should be left as no connects as GTL+ termination is provided on the processor silicon.
However, see
Unused active high inputs, should be connected through a resistor to ground (V
Unused outputs can be left unconnected; however, this may interfere with some TAP
functions, complicate debug probing, and prevent boundary scan testing. A resistor
must be used when tying bidirectional signals to power or ground. When tying any
signal to power or ground, a resistor will also allow for system testability. Resistor
values should be within ± 20% of the impedance of the motherboard trace for front
side bus signals. For unused GTL+ input or I/O signals, use pull-up resistors of the
same value as the on-die termination resistors (RT
TAP, GTL+ Asynchronous inputs, and GTL+ Asynchronous outputs do not include on-die
termination. Inputs and utilized outputs must be terminated on the motherboard.
Unused outputs may be terminated on the motherboard or left unconnected. Note that
leaving unused outputs unterminated may interfere with some TAP functions,
complicate debug probing, and prevent boundary scan testing.
All TESTHI[13:0] lands should be individually connected to V
that matches the nominal trace impedance.
The TESTHI signals may use individual pull-up resistors or be grouped together as
detailed below. A matched resistor must be used for each group:
• TESTHI[1:0]
• TESTHI[7:2]
• TESTHI8 – cannot be grouped with other TESTHI signals
• TESTHI9 – cannot be grouped with other TESTHI signals
• TESTHI10 – cannot be grouped with other TESTHI signals
• TESTHI11 – cannot be grouped with other TESTHI signals
• TESTHI12 – cannot be grouped with other TESTHI signals
• TESTHI13 – cannot be grouped with other TESTHI signals
However, using boundary scan test will not be functional if these lands are connected
together. For optimum noise margin, all pull-up resistor values used for TESTHI[13:0]
lands should have a resistance value within ± 20% of the impedance of the board
transmission line traces. For example, if the nominal trace impedance is 50 Ω, then a
value between 40 Ω and 60 Ω should be used.
16
Table 7
for details on GTL+ signals that do not include on-die termination.
Electrical Specifications
Chapter 4
for a land listing of the
). For details, see
T
via a pull-up resistor
TT
, V
,
CC
SS
).
SS
Table
16.
Datasheet
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