AM79C984 datasheet(12/44 Pages) AMD

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P R E L I M I N A R Y

Am79C984A

PIN DESCRIPTION

AUI Port

DI+, DI–

Data In

Differential Input

± are differential, Manchester receiver pins. The sig-

nals comply with IEEE 802.3, Section 7.

DO+, DO–

Data Out

Differential Output

± are differential, Manchester output driver pins.The

signals comply with IEEE 802.3, Section 7.

CI+, CI–

Collision Input

Differential Input/Output

± are differential, Manchester I/O signals. As an input,

CI is a collision-receive indicator. As an output, CI gen-

erates a 10-MHz signal if the eIMR device senses a

collision.

Twisted Pair Ports

TXD+0-3, TXD–0-3

Transmit Data

Differential Output

TXD

± are 10BASE-T port differential drivers (4 ports).

RXD+0-3, RXD–0-3

Receive Data

Differential Input

RXD

± are 10BASE-T port differential receive inputs

(4 ports).

Expansion Bus

DAT

Data

Input/Output/3-State

If the SELO and ACK pins are asserted during non-

collision conditions, the eIMR device drives NRZ data

onto the DAT line, regenerating the preamble if neces-

sary. During a collision, when JAM is HIGH, DAT is used

to differentiate between single-port (DAT=1) and multi-

port (DAT=0) collisions. DAT is an output when ACK is

asserted and the eIMR device’s ports are active; DAT

is an input when ACK is asserted and the ports are

inactive. If ACK is not asserted, DAT is in the high-im-

pedance state. It is recommended that DAT be pulled

up or down via a high value resistor.

JAM

Jam

Input/Output/3-State

The active eIMR device drives JAM HIGH, if it detects

a collision condition on one or more of its ports. The

state of the DAT pin is used in conjunction with JAM to

indicate a single port (DAT =1) or multiport (DAT=0) col-

lision. JAM is in the high-impedance state if neither the

SEL nor ACK signal is asserted. It is recommended that

JAM be pulled up or down via a high value resistor.

SELI0-1

Select In

Input, Active LOW

When the expansion bus is conﬁgured for Internal Arbi-

tration mode, these signals indicate that another eIMR

device is active; SELI0 or SELI1 is driven by SELO from

the upstream device. At reset, SELI0 selects between

the Internal Arbitration mode and the IMR+ mode of the

expansion bus; a HIGH selects the Internal Arbitration

mode and a LOW selects the IMR+ mode.

SELO

Select Out

Output, Active LOW

If the expansion bus is conﬁgured for Internal Arbitration

mode, an eIMR device drives this pin LOW when it is

active or when either of its SELI0-1 pins is LOW. An

active eIMR device is deﬁned as having one or more

ports receiving or colliding and/or is still transmitting

data from the internal FIFO, or extending a packet to the

minimum of 96 bit times. When the expansion bus is

conﬁgured for IMR+ mode, SELO is active when the

eIMR device is active (acquiring the functionality of the

REQ pin on the Am79C971 IMR+ device).

ACK

Acknowledge

Input/Output, Active LOW, Open Drain

This signal is asserted to indicate that an eIMR device

is active. It also signals to the other eIMR devices the

presence of a valid collision status on the JAM line and

valid data on the DAT line. When the eIMR device is

conﬁgured for Internal Arbitration mode, ACK is an I/O,

and must be pulled to VDD via a minimum equivalent

resistance of 1 k

Ω. When the eIMR device is conﬁgured

for IMR+ mode, ACK is an input driven by an external

arbiter.

COL

Collision

Input/Output, Active LOW, Open Drain

When asserted, COL indicates that more than one eIMR

device is active. Each eIMR device generates the Col-

lision Jam sequence independently. When the eIMR de-

vice is conﬁgured for Internal Arbitration mode, COL is

SELI_1

SELI_0

Arbitration

Mode

Internal

IMR+

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