AM79C973VCW datasheet(208/304 Pages) AMD

208 / 304 page

208

Am79C973/Am79C975

P R E L I M INARY

is programmed to use 16-bit soft-

ware structures for the descriptor

ring entries (BCR20, bits 7-0,

SWSTYLE is cleared to 0).

BAM

Broadcast Address Match is set

the

Am79C973/Am79C975

controller when it accepts the re-

ceived

frame,

because

the

frame’s destination address is of

the type ’Broadcast.’ BAM is valid

only when ENP is set. BAM is set

the

Am79C973/Am79C975

controller and cleared by the

host.

This bit does not exist when the

Am79C973/Am79C975 controller

is programmed to use 16-bit soft-

ware structures for the descriptor

ring entries (BCR20, bits 7-0,

SWSTYLE is cleared to 0).

19-16 RES

Reserved locations. These loca-

tions should be read and written

as zeros.

15-12 ONES

These four bits must be written as

ones. They are written by the host

and

unchanged

the

Am79C973/Am79C975

control-

ler.

11-0

BCNT

Buffer Byte Count is the length of

the buffer pointed to by this de-

scriptor, expressed as the two’s

complement of the length of the

buffer. This field is written by the

host

and

unchanged

the

Am79C973/Am79C975

control-

ler.

RMD2

Bit

Name

Description

ZERO

This

field

reserved.

The

Am79C973/Am79C975 controller

will write a zero to this location.

30-16 RFRTAG

Receive Frame Tag. Indicates

the Receive Frame Tag applied

from the EADI interface. This field

is user defined and has a default

value of all zeros. When RX-

FRTG (CSR7, bit 14) is set to 0,

RFRTAG will be read as all zeros.

See the section on Receive

Frame Tagging for details.

15-12 ZEROS

This

field

reserved.

Am79C973/Am79C975 controller

will write zeros to these locations.

11-0

MCNT

Message Byte Count is the length

in bytes of the received message,

expressed as an unsigned binary

integer. MCNT is valid only when

ERR is clear and ENP is set.

MCNT

written

the

Am79C973/Am79C975 controller

and cleared by the host.

RMD3

Bit

Name

Description

31-0

User Space. Reserved for user

defined space.

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