AM79C960KCW datasheet(78/127 Pages) AMD

78 / 127 page

P R E L I M I N A R Y

AMD

1-420

Am79C960

16907B-15

CRC

GEN

SEL

MUX

MATCH = 1:

Packet Accepted

MATCH = 0:

Packet Rejected

MATCH

Logical

Address

Filter

(LADRF)

Received Message

Destination Address

32-Bit Resultant CRC

Address Match Logic

The Logical Address Filter is used in multicast address-

ing schemes. The acceptance of the incoming frame

based on the filter value indicates that the message may

be intended for the node. It is the node’s responsibility to

determine if the message is actually intended for the

node by comparing the destination address of the stored

message with a list of acceptable logical addresses.

If the Logical Address Filter is loaded with all zeroes and

promiscuous mode is disabled, all incoming logical ad-

dresses except broadcast will be rejected.

The Broadcast address, which is all ones, does not go

through the Logical Address Filter and is handled as

follows:

1) If the Disable Broadcast Bit is cleared, the

broadcast address is accepted.

2) If the Disable Broadcast Bit is set and promiscuous

mode is enabled, the broadcast address is

accepted.

3) If the Disable Broadcast Bit is set and promiscous

mode is disabled, the broadcast address is rejected.

If external loopback is used, the FCS logic must be allo-

cated to the receiver (by setting the DXMTFCS bit in

CSR15, and clearing the ADD_FCS bit in TMD1) when

using multicast addressing.

PADR

This 48-bit value represents the unique node address

assigned by the IEEE and used for internal address

comparison. PADR[0] is the first address bit transmitted

on the wire, and must be zero. The six-byte nomencla-

ture used by the IEEE maps to the PCnet-ISA controller

PADR register as follows: the first byte comprises

PADR[7:0], with PADR[0] being the least significant bit

of the byte. The second IEEE byte maps to PADR[15:8],

again from LSbit to MSbit, and so on. The sixth byte

maps to PADR[47:40], the LSbit being PADR[40].

MODE

The mode register in the initialization block is copied into

CSR15 and interpreted according to the description of

CSR15.

Receive Descriptors

The Receive Descriptor Ring Entries (RDREs) are com-

posed of 4 receive message fields (RMD0-3). Together

they contain the following information:

s The address of the actual message data buffer in

user (host) memory.

s The length of that message buffer.

s Status information indicating the condition of the

buffer. The eight most significant bits of RMD1

(RMD1[15:0]) are collectively termed the STATUS

of the receive descriptor.

RMD0

Holds LADR [15:0]. This is combined with HADR [7:0] in

RMD1 to form the 24-bit address of the buffer pointed to

by this descriptor table entry. There are no restrictions

on buffer byte alignment or length.

RMD1

Bit

Name

Description

OWN

This bit indicates that the de-

scriptor entry is owned by the

host

(OWN=0)

the

PCnet-ISA controller (OWN=1).

The PCnet-ISA controller clears

the OWN bit after filling the buffer

pointed to by the descriptor entry.

The host sets the OWN bit after

emptying the buffer. Once the

PCnet-ISA controller or host has

relinquished

ownership

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