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Table 2-9. TYPDET#/VDDQ Relationship, always, How does the regulator switch?

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Layout/Routing Guidelines AGP 2.0 requires that these power planes be separate. In conjunction with the 4X data rate, the AGP 2.0 Interface Specification provides for low-voltage (1.5V) operation. The AGP 2.0 Specification implements a TYPEDET# (type detect) signal on the AGP connector that determines the operating voltage of the AGP 2.0 interface (VDDQ). The motherboard must provide either 1.5V or 3.3V to the add-in card depending on the state of the TYPEDET# signal (refer to Table 2-9. The 1.5V low-voltage operation applies ONLY to the AGP interface (VDDQ); VCC is always 3.3V. Note: The motherboard provides 3.3V to the Vcc pins of the AGP connector. If the graphics controller needs a lower voltage, then the add-in card must regulate the 3.3V VCC voltage to the controller's requirements. The graphics controller may ONLY power AGP I/O buffers with the VDDQ power pins. The TYPEDET# signal indicates whether the AGP 2.0 interface operates 1.5 volts or 3.3 volts. If TYPEDET# is floating (no connect) on an AGP add-in card, the interface is 3.3 volts. If TYPEDET# is shorted to ground, the interface is 1.5 volts. Table 2-9. TYPDET#/VDDQ Relationship TYPEDET# (on add-in card) VDDQ (supplied by MB) GND N/C 1.5V 3.3V As a result of this requirement, the motherboard must provide a flexible voltage regulator. This regulator must supply the appropriate voltage to the VDDQ pins on the AGP connector. For specific design recommendations, refer to the schematics in Appendix A, "Reference Design Schematics: Uni-Processor" and Appendix B, "Reference Design Schematics: Dual-Processor". VDDQ generation and AGP VREF generation must be considered together. Before developing VDDQ generation circuitry, refer to the AGP 2.0 Interface Specification. Figure 2-31 demonstrates one way to design the VDDQ voltage regulator. This regulator is a linear regulator with an external, low RDS-ON FET. The source of the FET is connected to 3.3V. This regulator will convert 3.3V to 1.5V or pass 3.3V depending on the state of TYPEDET#. If a linear regulator is used, it must draw power from 3.3V (not 5V) in order to control thermals (i.e., 5V regulated down to 1.5V with a linear regulator will dissipate approximately 7W at 2A). Because it must draw power from 3.3V and, in some situations, must simply pass that 3.3V to VDDQ (when a 3.3V add-in card is placed in the system), the regulator MUST use a low Rdson FET. AGP 1.0 modified VDDQ3.3min to 3.1V. Using an ATX power supply; the 3.3Vmin is 3.168V. Therefore, 68 mV of drop is allowed across the FET at 2A. This corresponds to a FET with an Rdson of 34 mW. How does the regulator switch? The feedback resistor divider is set to 1.5V. When a 1.5V card is placed in the system, the transistor is off and the regulator regulates to 1.5V. When a 3.3V card is placed in the system, the transistor is on, and the feedback is pulled to ground. When this happens, the regulator drives to gate of the FET to nearly 12V. This turns the FET on and passes 3.3V - 2A * RDS-ON to VDDQ. 2-38 Intel®820 Chipset Design Guide

Section	Page
Introduction 1	13
1.1 About This Design Guide	13
1.2 References	14
1.3 System Overview	14
1.3.1 Chipset Components	15
1.3.2 Bandwidth Summary	16
1.3.3 System Configuration	17
1.4 Platform Initiatives	20
1.4.1 Direct Rambus*	20
1.4.2 Streaming SIMD Extensions	20
1.4.3 AGP 2.0	20
1.4.4 Hub Interface	20
1.4.5 Manageability	21
1.4.6 AC’97	22
1.4.7 Low Pin Count (LPC) Interface	23
Layout/Routing Guidelines 2	27
2.1 General Recommendations	27
2.2 Component Quadrant Layout	27
2.3 Intel® 820 Chipset Component Placement	29
2.4 Core Chipset Routing Recommendations	30
2.5 Source Synchronous Strobing	31
2.6 Direct Rambus* Interface	33
2.6.1 Stackup	34
2.6.2 Direct Rambus* Layout Guidelines	34
2.6.2.1 RSL Routing	34
2.6.2.2 RSL Termination	37
2.6.2.3 Direct Rambus* Ground Plane Reference	39
2.6.2.4 Direct Rambus* Connector Compensation	40
2.6.2.5 RSL Signal Layer Alternation	46
2.6.2.6 Length Matching Methods	47
2.6.2.7 VIA Compensation	49
2.6.2.8 Length Matching & Via Compensation Example	49
2.6.3 Direct Rambus* Reference Voltage	51
2.6.4 High-speed CMOS Routing	51
2.6.4.1 SIO Routing	52
2.6.4.2 Suspend-to-RAM Shunt Transistor	52
2.6.5 Direct Rambus* Clock Routing	54
2.6.6 Direct Rambus* Design Checklist	54
2.7 AGP 2.0	57
2.7.1 AGP Interface Signal Groups	58
2.7.2 1X Timing Domain Routing Guidelines	59
2.7.3 2X/4X Timing Domain Routing Guidelines	59
2.7.4 AGP 2.0 Routing Summary	61
2.7.5 AGP Clock Routing	62
2.7.6 General AGP Routing Guidelines	62
2.7.7 VDDQ Generation and TYPEDET#	63
2.7.8 VREF Generation for AGP 2.0 (2X and 4X)	65
2.7.9 Compensation	67
2.7.10 AGP Pull-ups	67
2.7.10.1 AGP Signal Voltage Tolerance List	68
2.7.11 Motherboard / Add-in Card Interoperability	68
2.8 Hub Interface	69
2.8.1 Data Signals	70
2.8.2 Strobe Signals	70
2.8.3 HREF Generation/Distribution	70
2.8.4 Compensation	71
2.9 System Bus Design	72
2.9.1 100/133 MHz System Bus	72
2.9.2 System Bus Ground Plane Reference	73
2.10 S.E.C.C. 2 Grounding Retention Mechanism (GRM)	73
2.11 Processor CMOS Pullup Values	75
2.12 Additional Host Bus Guidelines	78
2.13 Ultra ATA/66	82
2.13.1 Ultra ATA/66 Detection	82
2.13.2 Ultra ATA/66 Cable Detection	83
2.13.3 Ultra ATA/66 Pullup/Pulldown Requirements	86
2.14 AC’97	87
2.14.1 AC’97 Signal Quality Requirements	89
2.14.2 AC’97 Motherboard Implementation	89
2.15 USB	91
2.16 ISA (82380AB)	92
2.16.1 ICH GPIO connected to 82380AB	92
2.16.2 Sub Class Code	92
2.17 IOAPIC Design Recommendation	92
2.18 SMBus/Alert Bus	93
2.19 PCI	93
2.20 RTC	93
2.20.1 RTC Crystal	94
2.20.2 External Capacitors	94
2.20.3 RTC Layout Considerations	95
2.20.4 RTC External Battery Connection	95
2.20.5 RTC External RTCRST Circuit	96
2.20.6 RTC Routing Guidelines	96
2.20.7 VBIAS DC Voltage and Noise Measurements	97
Advanced System Bus Design 3	101
3.1 Terminology and Definitions	101
3.2 AGTL+ Design Guidelines	104
3.2.1 Initial Timing Analysis	105
3.2.2 Determine General Topology, Layout, and Routing Desired	108
3.2.3 Pre-Layout Simulation	108
3.2.3.1 Methodology	108
3.2.3.2 Sensitivity Analysis	108
3.2.3.3 Monte Carlo Analysis	109
3.2.3.4 Simulation Criteria	109
3.2.4 Place and Route Board	110
3.2.4.1 Estimate Component To Component Spacing for AGTL+ Signals	110
3.2.4.2 Layout and Route Board	110
3.2.4.3 Host Clock Routing	112
3.2.4.4 APIC Data Bus Routing	112
3.2.5 Post-Layout Simulation	113
3.2.5.1 Intersymbol Interference	113
3.2.5.2 Cross-Talk Analysis	113
3.2.5.3 Monte Carlo Analysis	113
3.2.6 Validation	114
3.2.6.1 Measurements	114
3.2.6.2 Flight Time Simulation	114
3.2.6.3 Flight Time Hardware Validation	115
3.3 Theory	115
3.3.1 AGTL+	115
3.3.2 Timing Requirements	116
3.3.3 Cross-talk Theory	116
3.3.3.1 Potential Termination Cross-Talk Problems	118
3.4 More Details and Insight	119
3.4.1 Textbook Timing Equations	119
3.4.2 Effective Impedance and Tolerance/Variation	120
3.4.3 Power/Reference Planes, PCB Stackup, and High Frequency Decoupling	120
3.4.3.1 Power Distribution	120
3.4.3.2 Reference Planes and PCB Stackup	121
3.4.3.3 High Frequency Decoupling	122
3.4.3.4 SC242 Connector	123
3.4.4 Clock Routing	123
3.5 Definitions of Flight Time Measurements/ Corrections and Signal Quality	124
3.5.1 VREF Guardband	124
3.5.2 Ringback Levels	124
3.5.3 Overdrive Region	124
3.5.4 Flight Time Definition and Measurement	125
3.6 Conclusion	126
Clocking 4	129
4.1 Clock Generation	129
4.2 Component Placement and Interconnection Layout Requirements	134
4.2.1 14.318MHz Crystal to CK133	134
4.2.2 CK133 to DRCG	134
4.2.3 MCH to DRCG	135
4.2.4 DRCG to RDRAM Channel	136
4.2.5 Trace Length	136
4.3 DRCG Impedance Matching Circuit	138
4.3.1 DRCG Layout Example	139
4.4 AGP Clock Routing Guidelines	139
4.5 Series Termination Resistors for CK133 Clock Outputs	139
4.6 Unused Outputs	140
4.7 Decoupling Recommendation for CK133 and DRCG	140
4.8 DRCG Frequency Selection and the DRCG+	140
4.8.1 DRCG Frequency Selection Table and Jitter Specification	140
4.8.2 DRCG+ Frequency Selection Schematic	141
System Manufacturing 5	145
5.1 In Circuit FWH Flash BIOS Programming	145
5.2 FWH Flash BIOS Vpp Design Guidelines	145
5.3 Stackup Requirement	145
5.3.1 Overview	145
5.3.2 PCB Materials	146
5.3.3 Design Process	146
5.3.4 Test Coupon Design Guidelines	147
5.3.5 Recommended Stackup	147
5.3.6 Inner Layer Routing	147
5.3.7 Impedance Calculation Tools	148
5.3.8 Testing Board Impedance	148
5.3.9 Board Impedance/Stackup Summary	149
System Design Considerations 6	153
6.1 Power Delivery	153
6.1.1 Terminology and Definitions	153
6.1.2 Intel® 820 Chipset Customer Reference Board Power Delivery	154
6.1.3 64/72Mbit RDRAM Excessive Power Consumption	157
6.1.3.1 Option 1: Reduce the Clock Frequency During Initialization	158
6.1.3.2 Option 2: Increase the Current Capability of the 2.5V Voltage Regulator	158
6.2 Power Plane Splits	159
6.3 Thermal Design Power	159
6.4 Glue Chip 3 (Intel® 820 Chipset Glue Chip)	160
Appendix A: Reference Board Schematics: Uni-Processor	161
Reference Design Schematics: Uni-Processor A	163
Appendix B: Reference Design Schematics: Dual-Processor B	201

Match case Limit results 1 per page

Layout/Routing Guidelines

2-38

Intel

820 Chipset

Design Guide

AGP 2.0 requires that these power planes be separate. In conjunction with the 4X data rate, the

AGP 2.0 Interface Specification provides for low-voltage (1.5V) operation. The AGP 2.0

Specification implements a TYPEDET# (type detect) signal on the AGP connector that determines

the operating voltage of the AGP 2.0 interface (VDDQ). The motherboard must provide either

1.5V or 3.3V to the add-in card depending on the state of the TYPEDET# signal (refer to

Table 2-9

. The 1.5V low-voltage operation applies ONLY to the AGP interface (VDDQ); VCC is

always

3.3V.

Note:

The motherboard provides 3.3V to the Vcc pins of the AGP connector. If the graphics controller

needs a lower voltage, then the add-in card must regulate the 3.3V VCC voltage to the controller’s

requirements. The graphics controller may ONLY power AGP I/O buffers with the VDDQ power

pins.

The TYPEDET# signal indicates whether the AGP 2.0 interface operates 1.5 volts or 3.3 volts. If

TYPEDET# is floating (no connect) on an AGP add-in card, the interface is 3.3 volts. If

TYPEDET# is shorted to ground, the interface is 1.5 volts.

As a result of this requirement, the motherboard must provide a

flexible

voltage regulator. This

regulator must supply the appropriate voltage to the VDDQ pins on the AGP connector. For

specific design recommendations, refer to the schematics in

Appendix A, “Reference Design

Schematics: Uni-Processor”

and

Appendix B, “Reference Design Schematics: Dual-Processor”

VDDQ generation and AGP V

REF

generation must be considered together. Before developing

VDDQ generation circuitry, refer to the AGP 2.0 Interface Specification.

Figure 2-31

demonstrates one way to design the VDDQ voltage regulator. This regulator is a linear

regulator with an external, low R

DS-ON

FET. The source of the FET is connected to 3.3V. This

regulator will convert 3.3V to 1.5V or pass 3.3V depending on the state of TYPEDET#. If a linear

regulator is used, it must draw power from 3.3V (not 5V) in order to control thermals (i.e., 5V

regulated down to 1.5V with a linear regulator will dissipate approximately 7W at 2A). Because it

must draw power from 3.3V and, in some situations, must simply pass that 3.3V to VDDQ (when a

3.3V add-in card is placed in the system), the regulator MUST use a low R

dson

FET.

AGP 1.0 modified VDDQ3.3

min

to 3.1V. Using an ATX power supply; the 3.3V

min

is 3.168V.

Therefore, 68 mV of drop is allowed across the FET at 2A. This corresponds to a FET with an

dson

of 34 mW.

How does the regulator switch?

The feedback resistor divider is set to 1.5V. When a 1.5V card is

placed in the system, the transistor is off and the regulator regulates to 1.5V. When a 3.3V card is

placed in the system, the transistor is on, and the feedback is pulled to ground. When this happens,

the regulator drives to gate of the FET to nearly 12V. This turns the FET on and passes 3.3V - 2A *

DS-ON

to VDDQ.

Table 2-9. TYPDET#/VDDQ Relationship

TYPEDET# (on add-in card)

VDDQ (supplied by MB)

GND

1.5V

N/C

3.3V