Datasheet

Intel
®
Pentium
®
4 Processor on 0.13 Micron Process Datasheet 35
Electrical Specifications
2.12 AGTL+ System Bus Specifications
Routing topology recommendations may be found in the appropriate platform design guide listed
in Table 1-1. Termination resistors are not required for most AGTL+ signals because they are
integrated into the processor silicon.
Valid high and low levels are determined by the input buffers which compare a signal’s voltage
with a reference voltage called GTLREF (known as V
REF
in previous documentation).
Table 2-14 lists the GTLREF specifications. The AGTL+ reference voltage (GTLREF) should be
generated on the system board using high precision voltage divider circuits. It is important that the
system board impedance is held to the specified tolerance, and that the intrinsic trace capacitance
for the AGTL+ signal group traces is known and is well-controlled. For more details on platform
design, see the appropriate platform design guide.
NOTES:
1. Unless otherwise noted, all specifications in this table apply to all processor frequencies.
2. The tolerances for this specification have been stated generically to enable the system designer to calculate
the minimum and maximum values across the range of V
CC
.
3. GTLREF should be generated from V
CC
by a voltage divider of 1% tolerance resistors or 1% tolerance,
matched resistors. Refer to the appropriate Platform Design Guide
for implementation details.
4. R
TT
is the on-die termination resistance measured at V
OL
of the AGTL+ output driver. Refer to processor I/O
buffer models for I/V characteristics.
5. COMP resistance must be provided on the system board with 1% tolerance resistors. See the
appropriate
Platform Design Guide
for implementation details.
6. The V
CC
referred to in these specifications is the instantaneous V
CC
.
7. The specifications are for a platform to be forward compatible with future processors. A compatible platform
is one that is designed for some level of compatibility with future processors.
Table 2-14. AGTL+ Bus Voltage Definitions
Symbol Parameter Min Typ Max Units Notes
1
GTLREF Bus Reference Voltage 2/3 V
CC
–2% 2/3 V
CC
2/3 V
CC
+2% V 2, 3, 6
GTLREF
Compatible
Bus Reference Voltage 0.63 V
CC
–2% 0.63 V
CC
0.63 V
CC
+2% V 2, 3, 6, 7
R
TT
Termination Resistance 45 50 55 Ω 4
R
TT
Compatible
Termination Resistance 54 60 66
Ω 4, 7
COMP[1:0] COMP Resistance 50.49 51 51.51
Ω 5
COMP[1:0]
Compatible
COMP Resistance 61.3 61.9 62.5
Ω 5, 7
Figure 2-7. Test Circuit
2.4 nH
1.2 pF
Rload = 50 Ω
V
CC
V
CC
420 mils, 50 Ω, 169 ps/in