352 datasheet(28/95 Pages) INTEL

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Electrical Specifications

Datasheet

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 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 16 lists the GTLREF specifications. The GTL+

Reference voltage (GTLREF) should be generated on the system board using high

precision voltage divider circuits.

Table 16.

GTL+ Bus Voltage Definitions

Symbol

Parameter

Min

Typ

Max

Units Notes1

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

2,3

2. GTLREF is to be generated from VTT by a voltage divider of 1% resistors (one divider for each GTLREF

land).

3. For Intel 865 Express chipset LGA775 boards only, the GTLREF_PU should be 49.9 Ω 1%, and the GTLREF_PD should

be 100 Ω 1%.

GTLREF_PD

GTLREF pull down resistor

210 * 0.99

210

210 * 1.01

2,3

RPULLUP

On die pull-up for BOOTSELECT

signal

500

—

5000

4. These pull-ups are to VTT.

60 Ω Platform Termination

Resistance

5. RTT is the on-die termination resistance measured at VTT/2 of the GTL+ output driver. The IMPSEL land

is used to select a 50 Ω or 60 Ω buffer and RTT value.

50 Ω Platform Termination

Resistance

COMP[1:0]

60 Ω Platform Termination

COMP Resistance

59.8

60.4

COMP resistance must be provided on the system board with 1% resistors. COMP[1:0] resistors are

to VSS. COMP[5:4] resistors are to VTT.

50 Ω Platform Termination

COMP Resistance

49.9 * 0.99

49.9

49.9 * 1.01

COMP[5:4]

60 Ω Platform Termination

COMP Resistance

59.8

60.4

50 Ω Platform Termination

COMP Resistance

49.9 * 0.99

49.9

49.9 * 1.01

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