AM79C984 datasheet(29/44 Pages) AMD

29 / 44 page

P R E L I M I N A R Y

Am79C984A

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 10a. Notice that DI is connected to DO

of the MAC and DO is connected to DI of the MAC,

because the reverse conﬁguration only affects CI.

Where CI is an input in the normal mode, in the reverse

mode, CI is an output. Figure 10b shows the normal AUI

conﬁguration for reference.

Figure 10. AUI Port Interconnections

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

Ω. The DAT and

JAM pins also need to be pulled down via a high value

resistor. Refer to Figure 11.

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 12 shows

the conﬁguration for the IMR+ mode of operation.

DO+

DO–

DI+

DI–

CI+

CI–

DI+

DI–

DO+

DO–

CI+

CI–

DI+

DI–

DO+

DO–

CI+

CI–

DI+

DI–

DO+

DO–

CI+

CI–

a) Reverse Mode (with MAC)

b) Normal Mode (with MAU)

Am79C940

eIMR

Am7996

eIMR

0.1

µF

0.1

µF

0.1

µF

0.1

µF

39 – 150

Ω

0.1

µF

Ω

–9 V

1:1

20650A-16

20650B-15

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