AM79C988BJC datasheet(12/25 Pages) AMD

12 / 25 page

Am79C988A

PRELIMINARY

SYSTEMS APPLICATIONS

10BASE-T Repeaters

The IMR2/QuIET chipset provides a system solution to

designing 10BASE-T repeaters. Figure 3 shows the

necessary connections between the IMR2 device and

the QuIET device. Although only one QuIET device is

shown for clarity, three QuIET devices are required to

build a 12-port 10BASE-T repeater.

Port Switching

The IMR2/QuIET chipset supports port switching, which

is the ability to move individual ports to any one of mul-

tiple Ethernet backplanes under software control.To im-

plement port switching, each port on the QuIET device

is connected to two or more IMR2 devices in parallel.

Each IMR2 device deﬁnes a different logical repeater

and constitutes a separate Ethernet collision domain.

For each port on the QuIET device, only one corre-

sponding port on the IMR2 devices is enabled at any

one time.

Figure 4 shows the IMR2 device-to-QuIET device con-

nections necessary for port switching. Note that only

one QuIET device is shown for clarity. A full implemen-

tation would use three QuIET devices to provide 12

10BASE-T ports that can be individually switched be-

tween three Ethernet collision domains.

The IMR2 and QuIET devices must share a common

ground plane and a common power plane. Failure to

meet this design requirement may result in false asser-

tion of internal carrier sense or inability to unsquelch in

either PDI (for IMR2) or PDO (for QuIET).

Connection to Standard AUI Port

The PAUI ports on the QuIET device can also be con-

nected to standard AUI ports when used with devices

other than the IMR2 chip. Connection to a standard AUI

port is not meant to support a full length AUI cable. The

AUI connection should remain on the same board as

shown in Figure 6.

Connection to CMOS Circuits

The PAUI ports on the QuIET device can also drive

CMOS loads for other devices, including switches. The

PDO, PDI, and PCI signals connect directly to the

CMOS device. Note that CMOS mode must be

selected in the Management Command Frame.

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