Datasheet
Datasheet 31
Electrical Specifications
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 2-8 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 2-16 lists the GTLREF specifications. The GTL+ reference voltage
(GTLREF) must be generated on the motherboard using high precision voltage divider circuits.
Table 2-14. VTTPWRGD DC Specifications
Symbol Parameter Min Typ Max Unit Notes
V
IL
Input Low Voltage — — 0.3 V
V
IH
Input High Voltage 0.9 — — V
Table 2-15. BOOTSELECT and MSID[1:0] DC Specifications
Symbol Parameter Min Typ Max Unit Notes
V
IL
Input Low Voltage — — 0.24 V
1
NOTES:
1. These parameters are not tested and are based on design simulations.
V
IH
Input High Voltage 0.96 — — V -
Table 2-16. 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
2. GTLREF is to be generated from V
TT
by a voltage divider of 1% resistors (one divider for each GTLREF land).
GTLREF_PD GTLREF pull down resistor 210 * 0.99 210 210 * 1.01 Ω
2
R
PULLUP
On die pullup for
BOOTSELECT signal
500 - 5000 Ω
3
3. These pull-ups are to V
TT
.
R
TT
60 Ω Platform Termination
Resistance
41 50 58 Ω
4
4. R
TT
is the on-die termination resistance measured at V
TT
/2 of the GTL+ output driver. The IMPSEL pin is used to select a
50Ω or 60Ω buffer and R
TT
value.
50 Ω Platform Termination
Resistance
37 45 52 Ω
4
COMP[1:0]
60 Ω Platform COMP
Resistance
59.8 60.4 61 Ω
5
5. COMP resistance must be provided on the system board with 1% resistors. COMP[1:0] resistors are to V
SS
. COMP[3:2]
resistors are to V
SS
.
50 Ω Platform COMP
Resistance
49.9 * 0.99 49.9 49.9 * 1.01 Ω
5
COMP[3:2]
60 Ω Platform COMP
Resistance
59.8 60.4 61 Ω
5
50 Ω Platform COMP
Resistance
49.9 * 0.99 49.9 49.9 * 1.01 Ω
5