AM79C985 Advanced Micro Devices, AM79C985 Datasheet - Page 32

• Manufacturer Part Number: AM79C985
• Description: enhanced Integrated Multiport Repeater Plus (eIMR+)
• Manufacturer: Advanced Micro Devices

MAC Interface
The eIMR+ device can be connected directly to a MAC
through the AUI port. This requires that the AUI port be
configured in the reverse mode and connected as
shown in Figure 12a. Notice that DI is connected to DO
Internal Arbitration Mode Connection
The internal arbitration mode uses a modified daisy-
chain scheme to eliminate the need for any external
arbiter. In this mode, ACK and COL need to be pulled
up through a minimum resistance of 1 k
JAM pins also need to be pulled down via a high value
resistor. Refer to Figure 13.
32
Am79C940
DO+
DO–
DI+
DI–
CI+
CI–
0.1 F
a) Reverse Mode (with MAC)
40
RXD+
RXD–
40
40
40
40
100
40
0.1 F
Figure 12. AUI Port Interconnections
eIMR+
DI+
DI–
DO+
DO–
CI+
CI–
The DAT and
Figure 11. RXD Termination
P R E L I M I N A R Y
Am79C985
Am7996
39 – 150
DO+
DO–
DI+
CI+
DI–
CI–
1:1
of the MAC and DO is connected to DI of the MAC, be-
cause the reverse configuration only affects CI. Where
CI is an input in the normal mode, in the reverse mode,
CI is an output. Figure 12b shows the normal AUI con-
figuration for reference.
IMR+ Mode External Arbitration
The IMR+ mode maintains the full functionality of AMD’s
IMR+ (Am79C981) device’s expansion bus. In this
mode, the eIMR+ device requires external circuitry to
handle arbitration for control of the bus. Figure 14 shows
the configuration for the IMR+ mode of operation.
40
b) Normal Mode (with MAU)
–9 V
40
0.1 F
40
40
Twisted Pair
1:1
1:1
1:1
100
40
0.1 F
40
0.1 F
eIMR+
DI+
DI–
DO+
DO–
CI+
CI–
20650A-14
20650A-14
20651A-17
20651B-17
20651B-16