am79c984a Advanced Micro Devices, am79c984a Datasheet - Page 12

• Manufacturer Part Number: am79c984a
• Description: Enhanced Integrated Multiport Repeater Eimr
• Manufacturer: Advanced Micro Devices

PIN DESCRIPTION
AUI Port
DI+, DI–
Data In
Differential Input
DI are differential, Manchester receiver pins. The sig-
nals comply with IEEE 802.3, Section 7.
DO+, DO–
Data Out
Differential Output
DO are differential, Manchester output driver pins. The
signals comply with IEEE 802.3, Section 7.
CI+, CI–
Collision Input
Differential Input/Output
CI 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+
Transmit Data
Differential Output
TXD are 10BASE-T port differential drivers (4 ports).
RXD+
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
12
0-3
0-3
, TXD–
, RXD–
0-3
0-3
P R E L I M I N A R Y
Am79C984A
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.
SELI
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; SELI
the upstream device. At reset, SELI
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 SELI
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 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
0-1
SELI_1
X
X
0
SELI_0
or SELI
1
0
1
is driven by SELO from
0-1
Internal
IMR+
0
Arbitration
pins is LOW. An
selects between
Mode