Datasheet

Electrical Specifications
28 Datasheet
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 Table 8 for details on which GTL+ signals do not include on-die
termination.
Valid high and low levels are determined by the input buffers by comparing with a
reference voltage called GTLREF. Table 16 lists the GTLREF specifications. The GTL+
Reference voltage (GTLREF) should be generated on the system board using high
precision voltage divider circuits.
Table 16. GTL+ Bus Voltage Definitions
Symbol Parameter Min Typ Max Units Notes
1
NOTES:
1. Unless otherwise noted, all specifications in this table apply to all processor frequencies.
GTLREF_PU GTLREF pull up resistor 124 * 0.99 124 124 * 1.01 Ω
2,3
2. GTLREF is to be generated from V
TT
by a voltage divider of 1% resistors (one divider for each GTLREF
land).
3. For Intel 865 Express chipset LGA775 boards only, the GTLREF_PU should be 49.9 Ω 1%, and the GTLREF_PD should
be 100 Ω 1%.
GTLREF_PD GTLREF pull down resistor 210 * 0.99 210 210 * 1.01 Ω
2,3
R
PULLUP
On die pull-up for BOOTSELECT
signal
500 — 5000 Ω
4
4. These pull-ups are to V
TT
.
R
TT
60 Ω Platform Termination
Resistance
51 60 66 Ω
5
5. R
TT
is the on-die termination resistance measured at V
TT
/2 of the GTL+ output driver. The IMPSEL land
is used to select a 50 Ω or 60 Ω buffer and R
TT
value.
50 Ω Platform Termination
Resistance
39 50 55 Ω
5
COMP[1:0]
60 Ω Platform Termination
COMP Resistance
59.8 60.4 61 Ω
6
6. COMP resistance must be provided on the system board with 1% resistors. COMP[1:0] resistors are
to V
SS
. COMP[5:4] resistors are to V
TT
.
50 Ω Platform Termination
COMP Resistance
49.9 * 0.99 49.9 49.9 * 1.01 Ω
6
COMP[5:4]
60 Ω Platform Termination
COMP Resistance
59.8 60.4 61 Ω
6
50 Ω Platform Termination
COMP Resistance
49.9 * 0.99 49.9 49.9 * 1.01 Ω
6