Datasheet
27
Electrical Specifications
Valid high and low levels are determined by the input buffers by comparing with a
reference voltage called GTLREF.
Table 2-13
lists the GTLREF specifications. The GTL+
reference voltage (GTLREF) should be generated on the system board using high
precision voltage divider circuits. For more details on platform design, see the
applicable platform design guide.
NOTES:
1.
Unless otherwise noted, all specifications in this table apply to all processor frequencies.
2.
GTLREF is to be generated from VTT by a voltage divider of 1% resistors. If an Variable
GTLREF circuit is used on the board the GTLREF lands connected to the Variable GTLREF
circuit may require different resistor values. Each GTLREF land must be connected, refer to
the platform design guide for implementation details.
3.
R
TT
is the on-die termination resistance measured at V
TT
/3 of the GTL+ output driver.
Refer to the appropriate platform design guide for the board impedance. Refer to processor
I/O buffer models for I/V characteristics.
4.
COMP resistance must be provided on the system board with 1% resistors. See the
applicable platform design guide for implementation details. COMP[3:0] and COMP8
resistors are to V
SS
.
Table 2-13. GTL+ Bus Voltage Definitions
Symbol
Parameter
Min
Typ
Max
Units Notes
1
GTLREF_PU GTLREF pull up resistor
57.6 * 0.99
57.6
57.6 * 1.01
Ω
2
GTLREF_PD GTLREF pull down resistor
100 * 0.99
100
100 * 1.01
Ω
2
R
TT
Termination Resistance
45
50
55
Ω
3
COMP[3:0]
COMP Resistance
49.40
49.90
50.40
Ω
4
COMP8
COMP Resistance
24.65
24.90
25.15
Ω
4