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2.6.3.1
GTL+ Front Side Bus Specifications
In most cases, termination resistors are not required as these are integrated into the
processor silicon. See
termination.
Valid high and low levels are determined by the input buffers by comparing with a
reference voltage called GTLREF.
reference voltage (GTLREF) should be generated on the system board using high
precision voltage divider circuits.
Table 16.
GTL+ Bus Voltage Definitions
Symbol
GTLREF_PU
GTLREF_PD
R
PULLUP
R
TT
COMP[1:0]
COMP[5:4]
NOTES:
1. Unless otherwise noted, all specifications in this table apply to all processor frequencies.
GTLREF is to be generated from V
2.
GTLREF land).
3. These pull-ups are to V
4. R
is the on-die termination resistance measured at V
TT
to select a 50 Ω or 60 Ω buffer and R
5. COMP resistance must be provided on the system board with 1% resistors. COMP[1:0] resistors are to V
COMP[5:4] resistors are to V
28
Table 8
for details on which GTL+ signals do not include on-die
Table 16
Parameter
GTLREF pull up resistor
GTLREF pull down resistor
On die pull-up for
BOOTSELECT signal
60 Ω Platform Termination
Resistance
50 Ω Platform Termination
Resistance
60 Ω Platform Termination
COMP Resistance
50 Ω Platform Termination
COMP Resistance
60 Ω Platform Termination
COMP Resistance
50 Ω Platform Termination
COMP Resistance
by a voltage divider of 1% resistors (one divider for each
TT
.
TT
value.
TT
.
TT
lists the GTLREF specifications. The GTL+
Min
Typ
124 * 0.99
124
124 * 1.01
210 * 0.99
210
210 * 1.01
500
—
5000
51
60
39
50
59.8
60.4
49.9 * 0.99
49.9
49.9 * 1.01
59.8
60.4
49.9 * 0.99
49.9
49.9 * 1.01
/2 of the GTL+ output driver. The IMPSEL pin is used
TT
Electrical Specifications
1
Max
Units
Notes
2
Ω
2
Ω
3
Ω
4
66
Ω
4
55
Ω
5
61
Ω
5
Ω
5
61
Ω
5
Ω
SS
Datasheet
.
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