Intel 820E Benutzerhandbuch

70  

Design 

Guide 

The MCH AGP interface supports resistive buffer compensation (RCOMP). Tie the GRCOMP pin to a 
40 

Ω,

 2% (or 39-

Ω

, 1%) pull-down resistor (to ground), via a 10 mil-wide, very short (<0.5 inch) trace. 

AGP control signals require pull-up resistors to V

DDQ

 on the motherboard, to ensure that they maintain 

stable values when no agent is actively driving the bus. The signals requiring pull-up resistors are: 

• 

1

×

 timing domain signals 

 

FRAME# 

 

TRDY# 

 

IRDY# 

 

DEVSEL# 

 

STOP# 

 

SERR# 

 

PERR# 

 

RBF# 

 

PIPE# 

 

REQ# 

 

WBF# 

 

GNT# 

 

ST[2:0] 

It is critical that these signals be pulled up to V

DDQ

 (not 3.3 V). 

The trace stub to the pull-up resistor on 1

×

 timing domain signals should be kept at less than 

0.5 inch, to avoid signal reflections from the stub. 
The strobe signals require pull-up/pull-downs on the motherboard, to ensure that they maintain 
stable values when no agent is driving the bus. 

Note:  INTA# and INTB# should be pulled to 3.3 V, not V

DDQ

. 

• 

2

×

/4

×

 timing domain signals 

 

AD_STB[1:0] 

(pull-up to V

DDQ

) 

 

SB_STB  

(pull-up to V

DDQ

) 

 

AD_STB[1:0]#  (pull-down to ground) 

 

SB_STB# 

(pull-down to ground) 

The trace stub to the pull-up/pull-down resistor on 2

×

/4

×

 timing domain signals should be kept to 

less than 0.1 inch, to avoid signal reflections from the stub. 
The pull-up/pull-down resistor value requirements are shown in the following table. 
 

4 k

Ω 

16 k

Ω 

The recommended AGP pull-up/pull-down resistor value is 8.2 k

Ω

.