Intel Pentium III BX80526U600256E User Manual
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Product codes
BX80526U600256E
36
Datasheet
Pentium
®
III Processor for the PGA370 Socket at 500 MHz to 1.13 GHz
2.11
AGTL / AGTL+ System Bus Specifications
It is recommended that the AGTL+ bus be routed in a daisy-chain fashion with termination
resistors to V
resistors to V
TT
. These termination resistors are placed electrically between the ends of the signal
traces and the V
TT
voltage supply and generally are chosen to approximate the system platform
impedance. The valid high and low levels are determined by the input buffers using a reference
voltage called V
voltage called V
REF
. Refer to the appropriate platform design guide for more information
Table 12
below lists the nominal specification for the AGTL+ termination voltage (V
TT
). The
AGTL+ reference voltage (V
REF
) is generated on the system motherboard and should be set to 2/3
V
TT
for the processor and other AGTL+ logic. It is important that the baseboard impedance be
specified and held to a ±15% tolerance, and that the intrinsic trace capacitance for the AGTL+
signal group traces is known and well-controlled. For more details on the AGTL+ buffer
specification, see the Intel
signal group traces is known and well-controlled. For more details on the AGTL+ buffer
specification, see the Intel
®
Pentium
®
II Processor Developer's Manual and AP-585,
Intel
®
Pentium
®
II Processor AGTL+ Guidelines.
NOTES:
1. Unless otherwise noted, all specifications in this table apply to Pentium III processors at all frequencies.
2. Pentium III processors for the PGA370 socket contain AGTL+ termination resistors on the processor die,
2. Pentium III processors for the PGA370 socket contain AGTL+ termination resistors on the processor die,
except for the RESET# input.
3. V
TT
and Vcc
1.5
must be held to 1.5 V ±9%. It is required that V
TT
and Vcc
1.5
be held to 1.5 V ±3% while the
processor system bus is idle (static condition). This is measured at the PGA370 socket pins on the bottom
side of the baseboard.
side of the baseboard.
4. The value of the on-die R
TT
is determined by the resistor value measured by the RTTCTRL signal pin. See
Section 7.0
for more details on the RTTCTRL signal. Refer to the recommendation guidelines for the specific
chipset/processor combination.
5. V
REF
is generated on the motherboard and should be 2/3 V
TT
±2% nominally. Insure that there is adequate
V
REF
decoupling on the motherboard.
NOTES:
1. Specifications in this table do not apply to Pentium III processors at all frequencies. Please refer to the
Intel
®
Pentium
®
III Processor Specification Update for a complete listing on the processors that support the
AGTL specification.
2. Pentium III processors for the PGA370 socket contain AGTL termination resistors on the processor die,
except for the RESET# input.
3. V
TT
must be held to 1.25 V ±9%. It is required that V
TT
be held to 1.25 V ±3% while the processor system bus
is idle (static condition). This is measured at the PGA370 socket pins on the bottom side of the baseboard.
4. The value of the on-die R
TT
is determined by the resistor value measured by the RTTCTRL signal pin. The
on-die R
TT
has a resistance tolerance of ±15%. See
Section 7.0
for more details on the RTTCTRL signal.
Refer to the recommendation guidelines for the specific chipset/processor combination.
5. V
REF
is generated on the motherboard and should be 2/3 V
TT
±2% nominally. Insure that there is adequate
V
REF
decoupling on the motherboard.
6. For the Coppermine-T differential clock platform, the on-die RTT min should be 50
Ω
.
7. Coppermine-T UP platforms require a 56
Ω
resistor and Coppermine-T DP platforms require a 68
Ω
resistor.
Tolerance for the on-die R
TT
is ±10% for 56
Ω
and 68
Ω
resistors and ±15% for 100
Ω
resistors
Table 12. Processor AGTL+ Bus Specifications
1, 2
Symbol
Parameter
Min
Typ
Max
Units
Notes
V
TT
Bus Termination Voltage
1.50
V
3
On-die R
TT
Termination Resistor
40
130
Ω
4
V
REF
Bus Reference Voltage
0.950
2/3 V
TT
1.05
V
5
Table 13. Processor AGTL Bus Specifications
1, 2
Symbol
Parameter
Min
Typ
Max
Units
Notes
V
TT
Bus Termination Voltage
1.14
1.25
1.308
V
3
On-die R
TT
Termination Resistor
50
6
56, 68
115
Ω
4, 7
V
REF
Bus Reference Voltage
2/3 V
TT
- 2%
2/3 V
TT
2/3 V
TT
+ 2%
V
5