AM79C985JC datasheet(12/48 Pages) AMD

12 / 48 page

Am79C985

PRELIMINARY

PIN DESCRIPTION

AUI Port

DI+, DI–

Data In

Differential Input

± are differential, Manchester receiver pins. The

signals 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 Am79C981 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 Collision Jam sequence independently. When the

eIMR+ device is conﬁgured for Internal Arbitration

SELI_1

SELI_0

Arbitration

Mode

Internal

IMR+

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