AM79C974 datasheet(40/153 Pages) AMD

Part #	AM79C974

Description	PCnetTM-SCSI Combination Ethernet and SCSI Controller for PCI Systems

PDF	153 Pages

Scroll/Zoom	100%

Manufacturer	AMD [Advanced Micro Devices]

Direct Link	http://www.amd.com

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40 / 153 page

AMD

P R E L I M I N A R Y

Am79C974

Master Initiated Termination

There are three scenarios besides normal completion of

a transaction where the Am79C974 controller will termi-

nate the cycles it produces on the PCI bus. These are

Preemption with and without

FRAME assertion and

Master Abort.

Preemption When FRAME is Deasserted

The Am79C974 controller can generate multiple ad-

dress phases during a single bus ownership period

when transferring data.

FRAME is deasserted in be-

tween two address phases. While

FRAME is deass-

erted, the central arbiter can remove

GNT to the

Am79C974 controller at any time to service another

master. When

GNT is removed, the Am79C974 control-

ler will finish the current transfer and then release the

bus. It will keep

REQ asserted to regain bus ownership

as soon as possible.

18681A-18

FRAME

CLK

IRDY

TRDY

DEVSEL

REQ

GNT

1234567

ADDR

BE's

0111

PAR

DATA

DEVSEL is sampled by the Am79C974 controller.

Figure 14. Preemption When FRAME is Deasserted

AM79C974 Datasheet(PDF) 40 Page - Advanced Micro Devices

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