AM79C982 datasheet(18/26 Pages) AMD

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Am79C982

SET (Write) Opcodes

bIMR Chip Programmable Options

SI data:

0000 10SA

SO data:

None

bIMR Chip Programmable Options can be enabled (dis-

abled) by setting (resetting) the appropriate bit in the

command string. The two programmable bits are:

S—AUI SQE Test Mask, and A—Alternative Port Activ-

ity Monitor (PAM) Function. These options can be en-

abled (disabled) by setting (resetting) the appropriate bit

in the command string.

S—AUI SQE Test Mask

Setting this bit allows the bIMR chip to ignore activity on

the CI signal pair, in the SQE Test Window, following a

transmission on the AUI port. This event occurs when

the attached MAU has the SQE Test option enabled,

therefore generating a burst of CI activity following every

transmission. This is interpreted by the bIMR device as

a collision, causing the bIMR device to generate a full

Jam pattern. Although the MAU attached to a repeater is

required not to have its SQE test function active, this is a

common installation error, causing difficulty in diagnos-

ing network throughput problems.

The SQE Test Window, as defined by the IEEE 802.3

(Section 7.2.2.2.4), is from 6-bit times to 34-bit times

(0.6

µs to 3.4 µs). This includes delay introduced by a

50 m AUI. CI activity that occurs outside this window is

not ignored and is treated as true collision.

Note that enabling this function does not prevent the re-

porting of this condition by the bIMR device and the two

functions operate independently.

A—Alternative Port Activity Monitor (PAM)

Function

Setting the Alternative Port Activity Monitor Function al-

lows the PAM function to be altered such that the Carrier

Sense data is presented unmodified. In default opera-

tion the PAM output (Carrier Sense bits in the CRS bit

stream) are masked if the port is either disabled or parti-

tioned. This does not allow the Repeater Management

software to sense activity on all segments at all times.

The ability to monitor partitioned or disabled ports allows

fault tolerance to be built into the Repeater Management

software.

Alternate AUI Port Partitioning Algorithm

SI data:

00011111

SO data:

None

The AUI port Partitioning/Reconnection scheme can be

programmed for the alternate (transmit only) reconnec-

tion algorithm by invoking this command. To return the

AUI back to the standard (transmit or receive) reconnec-

tion algorithm, it is necessary to reset the bIMR device.

Standard partitioning algorithm is selected upon reset.

Alternate TP Ports Partitioning Algorithm

SI data:

00010000

SO data:

None

The TP ports Partitioning/Reconnection scheme can be

programmed for the alternate (transmit only) reconnec-

tion algorithm by invoking this command. All TP ports

are affected as a group by this command. To return the

TP ports back to the standard (transmit or receive) re-

connection algorithm, it is necessary to reset the bIMR

device. The standard partitioning algorithm is selected

upon reset.

AUI Port Disable

SI data:

00101111

SO data:

None

The AUI port will be disabled upon receiving this com-

mand. Subsequently, the bIMR chip will ignore all inputs

(Carrier Sense and SQE) appearing at the AUI port and

will not transmit any data or Jam Sequence on the AUI

port. Issuing this command will also cause the AUI port

to have its internal partitioning state machine forced to

its idle state. Therefore, a Partitioned Port may be re-

connected by first disabling and then re-enabling

the port.

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