Datasheet

Datasheet 27
Electrical Specifications
2.7.3.1 GTL+ Front Side Bus Specifications
In most cases, termination resistors are not required as these are integrated into the
processor silicon. See Table 9 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 14 lists the GTLREF specifications for both
50 Ohm and 60 Ohm platforms. The GTL+ reference voltage (GTLREF) should be
generated on the system board using high precision voltage divider circuits.
NOTES:
1. Unless otherwise noted, all specifications in this table apply to all processor frequencies.
2. GTLREF is to be generated from V
TT
by a voltage divider of 1% resistors (one divider for
each GTLEREF land).
3. R
TT
is the on-die termination resistance measured at V
TT
/3 of the GTL+ output driver.
4. COMP resistance must be provided on the system board with 1% resistors. COMP[3:0] and
COMP8 resistors are to V
SS
.
Table 14. GTL+ Bus Voltage Definitions
Symbol Parameter Min Typ Max Units Notes
1
GTLREF_PU GTLREF pull up resistor 124 * 0.99 124 124 * 1.01 Ω
GTLREF_PD GTLREF pull down resistor 210 * 0.99 210 210 * 1.01 Ω 2, 4
R
TT
Termination Resistance 45 50 55 Ω 3
COMP[3:0]
60 Ω Platform termination
Resistance
60.4 * 0.99 60.4 60.4 * 1.01 Ω 4
50 Ω Platform termination
Resistance
49.9 * 0.99 49.9 49.9 * 1.01 Ω 4
COMP8
60 Ω Platform termination
Resistance
30.1 * 0.99 30.1 30.1 * 1.01 Ω 4
50 Ω Platform termination
Resistance
24.9 * 0.99 24.9 24.9 * 1.01 Ω 4