82375EB datasheet(77/131 Pages) INTEL

77 / 131 page

82375EBSB

290477 – 57

Figure 15 Access to Locked Target with PLOCK

Asserted During Address Phase

519 DEVICE SELECTION

The PCEB asserts DEVSEL

to indicate that it is the target of the PCI transaction DEVSEL

is asserted

when the PCEB as a target positively subtractively or negatively (82374SB only) decodes the PCI transac-

tion In all cases except one once the PCEB asserts DEVSEL

the signal remains asserted until FRAME

negated (IRDY

is asserted) and either STOP

or TRDY

is asserted The exception is a target abort

described in Section 5110 Transaction Termination

For most systems PCI target devices are able to complete a decode and assert DEVSEL

within 2 or 3

clocks of FRAME

(medium and slow in the Figure 16) Accordingly since the PCEB subtractively or nega-

tively (82374SB only) decodes all unclaimed PCI cycles (except configuration cycles) it provides a configura-

tion option to reduce by 1 clock the edge at which it samples DEVSEL

allowing faster access to the

expansion bus Use of this option is limited by the slowest positive decode agent on the bus This is described

in more detail in Section 40 Address Decoding

82375EB Datasheet(PDF) 77 Page - Intel Corporation