AM79C985JC datasheet(26/48 Pages) AMD

26 / 48 page

Am79C985

PRELIMINARY

SET (Write Commands)

Chip Programmable Options

SI Data

0000 1CSA

SO Data (Pri)

None

SO Data (Sec)

None

The eIMR+ chip programmable options can be enabled

(or disabled) by setting (or resetting) one or more of the

C, S, and A bits in the command string. The three pro-

grammable options are C - CI Reporting, S - AUI test

mask, and A - Alternate port activity monitor (PAM)

function.

HIMIB Connection

This bit, when set, indicates to the eIMR+ device that it

is connected to a HIMIB device.

AUI SQE Test Mask

Setting this bit allows the eIMR+ chip to ignore activity

on the CI signal pair, during the SQE test window, fol-

lowing a transmission on the AUI port. Enabling this

function does not prevent the reporting of this condi-

tion by the eIMR+ device. The two functions operate

independently.

The SQE Test Window, as deﬁned in IEEE 802.3 (Sec-

tion 7.2.2.2.4) is from 6 bit times to 34 bit times (0.6

µs

to 3.4

µs). This includes the delay introduced by a 50-

m AUI. CI activity that occurs outside this window is not

ignored and is treated as a true collision.

Alternate Port Activity Monitor Function

Setting this bit causes the Port Activity Monitor (PAM)

function to be altered such that the CRS data is pre-

sented unmodiﬁed. In default operation, CRS is

masked if the port is either disabled or partitioned. Note

that the HIMIB device resets this bit (default operation).

Alternate AUI Partitioning Algorithm

SI Data

0001 1111

SO Data (Pri)

None

SO Data (Sec)

None

Invoking this command sets the partition/reconnection

scheme for the AUI port to the alternate (transmit-only)

reconnection algorithm. To return the AUI port to the

standard (transmit or receive) reconnection algorithm,

it is necessary to reset the eIMR+ device. The standard

partitioning algorithm is selected on reset. If two eIMR+

devices are connected, this command sets both AUI

ports.

Alternate TP Partitioning Algorithm

SI Data

0001 0000

SO Data (Pri)

None

SO Data (Sec)

None

Invoking this command sets the partition/reconnection

scheme for the TP ports to the alternate (transmit-only)

reconnection algorithm. To return the TP ports to the

standard (transmit or receive) reconnection algorithm,

it is necessary to reset the eIMR+ device. The standard

partitioning algorithm is selected on reset.

Primary AUI Port Disable

0010 1111

SO Data (Pri)

None

SO Data (Sec)

None

This command disables the AUI port on the primary

eIMR+ device. Subsequently the eIMR+ chip will ig-

nore all inputs to this port and will not transmit a DAT or

JAM pattern on the AUI port. Disabling the AUI port

also sets the partitioning state machine of the AUI port

to the idle state. Therefore, a partitioned port can be re-

connected by ﬁrst disabling the AUI port and then en-

abling the AUI port.

The AUI port on the primary eIMR+ device defaults to

enabled on reset.

Secondary AUI Port Disable

SI Data

0010 1110

SO Data (Pri)

None

SO Data (Sec)

None

This command disables the AUI port on the eIMR+ de-

vice designated as the secondary HIMIB attachment.

Subsequently the eIMR+ chip will ignore all inputs to

this port and will not transmit a DAT or JAM pattern on

the AUI port. Disabling the AUI port also sets the parti-

tioning state machine of the AUI port to the idle state.

Therefore, a partitioned port can be reconnected by ﬁrst

disabling the AUI port and then enabling the AUI port.

The AUI port on the secondary eIMR+ device defaults

to enabled on reset.

Primary AUI Port Enable

0011 1111

SO Data (Pri)

None

SO Data (Sec)

None

This command enables the AUI port on the primary

eIMR+ device.

Secondary AUI Port Enable

SI Data

0011 1110

SO Data (Pri)

None

SO Data (Sec)

None

This command enables the AUI port on the eIMR+ de-

vice designated as the secondary HIMIB attachment.

When enabled, the secondary AUI port is fully func-

tional, and can be controlled by the serial/management

interface. However, when used with the Am79C987 de-

vice, no status is displayed for this port since the HIMIB

device does not manage this port. At reset, this port is

enabled.

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