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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 (R
TAP and CMOS signals do not include on-die termination. Inputs and used 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[12,10:0] lands should be individually connected to V
resistor 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/FC42 – cannot be grouped with other TESTHI signals
• TESTHI9/FC43 – cannot be grouped with other TESTHI signals
• TESTHI10 – cannot be grouped with other TESTHI signals
• TESTHI12/FC44 – cannot be grouped with other TESTHI signals
Terminating multiple TESTHI pins together with a single pull-up resistor is not
recommended for designs supporting boundary scan for proper Boundary Scan testing
of the TESTHI signals. For optimum noise margin, all pull-up resistor values used for
TESTHI[12,10:0] 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
, then a value between 40
2.5
Power Segment Identifier (PSID)
Power Segment Identifier (PSID) is a mechanism to prevent booting under mismatched
power requirement situations. The PSID mechanism enables BIOS to detect if the
processor in use requires more power than the platform voltage regulator (VR) is
capable of supplying. For example, a 130 W TDP processor installed in a board with a
65 W or 95 W TDP capable VR may draw too much power and cause a potential VR
issue.
16
Table 7
for details on GTL+ signals that do not include on-die termination.
and 60
Chapter 4
for a land listing of the
). For details see
TT
TT
should be used.
Electrical Specifications
, V
,
CC
SS
).
SS
Table
14.
using a pull-up
Datasheet
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