AM79C985JC datasheet(23/48 Pages) AMD

23 / 48 page

Am79C985

PRELIMINARY

When two eIMR+ devices are connected to one HIMIB

device, the secondary device transmits the status of its

TP ports, then transmits the status of the primary eIMR+

TP ports and AUI port (CRS and CI). Note that the sec-

ondary device does not transmit the status of its AUI

port. At Reset, the secondary device (and single eIMR+

device) internally synchronizes the CRS stream to begin

with the AUI CI bit. SO is the eIMR+ device response to

a Get command.

The pins SI_D and CRS_I are multi-purpose pins. Their

primary purpose is management input to the primary

eIMR+ device. They are also used to set the manage-

ment mode of the eIMR+ device. The mode is set on the

rising edge of RST. The settings are shown in Table 4.

Following reset, the eIMR+ devices retain their manage-

ment designations. However, CRS_I and SI_D return to

their management port functions.

Command/Response Timing

Figure 7 shows the command/response timing. At the

end of a GET command, the eIMR+ device waits two

SCLK cycles and then transmits the response on SO.

The secondary eIMR+ device stores the data received

on the SI_D input (from the primary eIMR+ device) in

an internal register. When it has transmitted D3 data, it

appends the received response to the end of the SO

signal.

Following reset, after the eIMR+ devices have been as-

signed their primary and secondary designation, SO

and SI_D return to their management-port functions.

Port Activity

In addition to providing a means for receiving com-

mands and sending data in response to those com-

mands, the management port includes a CRS signal

that transmits the state of the eIMR+ device’s internal

carrier-sense signals.

When two eIMR+ devices are connected to one

Am79C987 HIMIB device (as shown in the

System

Applications section), CRS_I of the secondary device

receives the following signals from the primary device:

the carrier-sense signals of the AUI port, the CI-bit sta-

tus of the AUI port, and the carrier-sense signals of the

TP ports. The secondary device transmits the status of

the AUI port (CRS and CI) for the primary device, the

status of its own TP ports (TP0-TP3), and then the sta-

tus of the primary device’s TP ports (TP4-TP7). The

status of the AUI port of the secondary device is not

retransmitted (see Figure 8).

Figure 7. Management Get Command/Response

Table 4. eIMR+ Device Management Designations

Two eIMR+ Devices

CRS_I

SI_D

Single eIMR+ Device

Primary eIMR+ Device

Secondary eIMR+ Device

√

Note: For SO on the Primary device, D[3:0] corresponds to TP[7:4].

ST D0 D1 D2 D3 D4 D5 D6 D7

ST D0 D1 D2 D3

SCLK

Primary eIMR+ Device or

Single eIMR+ Device

ST D0 D1 D2 D3 D4 D5 D6 D7

Secondary eIMR+ Device

20651B-12

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