AM79C976 datasheet(231/309 Pages) AMD

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8/01/00

Am79C976

231

P R E L I M INARY

421

LAFM

Logical Address Filter Match is set by the Am79C976 controller when it accepts the

received frame based on the value in the logical address filter register. LAFM is valid

only when ENP is set. LAFM is set by the Am79C976 controller and cleared by the

host.

Note that if DRCVBC (CSR15, bit 14) is cleared to 0, only BAM, but not LAFM will be

set when a Broadcast frame is received, even if the Logical Address Filter is

programmed in such a way that a Broadcast frame would pass the hash filter. If

DRCVBC is set to 1 and the Logical Address Filter is programmed in such a way that

a Broadcast frame would pass the hash filter, LAFM will be set on the reception of a

Broadcast frame.

This bit does not exist when the Am79C976 controller is programmed to use 16-bit

software structures for the descriptor ring entries (BCR20, bits 7-0, SWSTYLE is

cleared to 0).

BAM

Broadcast Address Match is set by the Am79C976 controller when it accepts the

received frame, because the frame’s destination address is of the type ’Broadcast.’

BAM is valid only when ENP is set. BAM is set by the Am79C976 controller and

cleared by the host.

This bit does not exist when the Am79C976 controller is programmed to use 16-bit

software structures for the descriptor ring entries (BCR20, bits 7-0, SWSTYLE is

cleared to 0).

19-16

Reserved.

415-0

BCNT

Buffer Byte Count is the length of the buffer pointed to by this descriptor, expressed

as the two’s complement of the length of the buffer. This field is written by the host

and unchanged by the Am79C976 controller.

Reserved.

30-16

RFRTAG[14:0]

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

RXFRTG (CSR7, bit 14) is set to 0, RFRTAG will be read as all zeros. See the section

on Receive Frame Tagging for details.

15-0

MCNT

Message Byte Count is the number of bytes of the received message written to the

receive buffer. This is the actual frame length (including FCS) unless stripping is

enabled and the length field is < 46 bytes. In this case, MCNT is 14 + length_field.

MCNT can take values in the range 15 to 59 and values greater than or equal to 64.

MCNT is expressed as an unsigned binary integer. MCNT is valid only when ERR is

clear and ENP is set. MCNT is written by the Am79C976 controller and cleared by

the host.

0Ch

31:0

USER SPACE

User Space. Reserved for user defined data.

Offset

Bit

Name

Description

AM79C976 Datasheet(PDF) 231 Page - Advanced Micro Devices

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