Intel 21555 manual Clamping Voltage, Introduction, Clock Configuration Jumpers, Voltage Clampa

Introduction

1.6.1Clock Configuration

Table 3 describes the resistor jumpers to install that connect p_clk and s_clk_o to the Mictor connectors. To improve signal integrity and minimize noise, these signals are not wired to the Mictor connectors. Resistor jumpers also control the selection of clock signals. See Figure 3 on page 10 for the resistor jumper locations. See Table A-3 on page 24 for Mictor pinouts.

Table 3. Clock Configuration Jumpers

Clock Source	Installed	Removed
Use the s_clk_o signal from the 21555 as the local	R65, R73	R68, R93
clock.
Use the s_clk_i that is the output of the clock buffer	R73	R68
as the local clock.
Use the system slot to drive the 21555 s_clk_i.	R68	R73
Use an oscillator as the asynchronous local clock.	R93	R65, R68
Use the system slot to provide the local clock.	R92, R116, R69	R91, R115, R72
Use the clock buffer to provide the local clock.	R91, R115, R72	R92, R116, R69

1.6.2Clamping Voltage

Table 4 gives the clamping voltage resistor jumper configurations. These jumper resistors designate the DE1B55503 as a 3.3V or a 5V PCI device. A mix of 3.3 and 5 V cards is not allowed. The E1 regulator provides the 3.3V or 5 V clamping voltage for the local bus. The resistor jumpers connect s_vio to either 3.3V or 5V. Figure 4 on page 12 shows the location of the resistor jumpers.

Table 4. Voltage Clampa

Function	Installed	Removed
s_vio is 3.3V	R95	R97
s_vio is 5V	R97	R95

a.Only one jumper resistor (R95 or R97) may be installed at a time. Installing both or no jumper resistors is not allowed.

21555 PCI-to-PCI Bridge Evaluation Board User’s Guide 11