DP83905AVQB National Semiconductor, DP83905AVQB Datasheet - Page 43

• Manufacturer Part Number: DP83905AVQB
• Description: IC CONTROLR AT/LAN TP IN 160PQFP
• Manufacturer: National Semiconductor
• Series: AT/LANTIC™r

Specifications of DP83905AVQB

• Controller Type: AT, LAN Twisted-Pair Interface Controller
• Voltage - Supply: 4.75 V ~ 5.25 V
• Current - Supply: 100mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 160-BFQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Interface: -
• Other names: *DP83905AVQB

5 0 Register Descriptions
bits to set in the multicast registers All multicast filter bits
that correspond to multicast address accepted by the node
are then set to one To accept all multicast packets all of
the registers are set to all ones
Note Although the hashing algorithm does not guarantee pertect filtering of
6 0 Operation of AT LANTIC
Controller
This section details the operation of the AT LANTIC Con-
troller The operations discussed are packet reception and
transmission bus operations and loopback diagnostics
6 1 TRANSMIT RECEIVE PACKET ENCAPSULATION
DECAPSULATION
A standard IEEE 802 3 packet consists of the following
fields preamble Start of Frame Delimiter (SFD) destination
address source address length data and Frame Check
Sequence (FCS) The typical format is shown in the figure
following The packets are Manchester encoded and decod-
ed by the ENDEC module and transferred serially to the NIC
module using NRZ data with a clock All fields are of fixed
length except for the data field The AT LANTIC Controller
generates and appends the preamble SFD and FCS field
during transmission The Preamble and SFD fields are
stripped during reception (The CRC is passed through to
buffer memory during reception )
multicast address it will pertectly filter up to 64 multicast addresses if
these addresses are chosen to map into unique locations in the multi-
cast filter
FIGURE 25 Multicast Addressing
FIGURE 26 Ethernet Packet
(Continued)
TL F 11498– 22
TL F 11498– 23
43
PREAMBLE AND START OF FRAME DELIMITER (SFD)
The Manchester encoded alternating 1 0 preamble field is
used by the ENDEC to acquire bit synchronization with an
incoming packet When transmitted each packet contains
62 bits of alternating 1 0 preamble Some of this preamble
will be lost as the packet travels through the network The
preamble field is stripped by the NIC module Byte align-
ment is performed with the Start of Frame Delimiter (SFD)
pattern which consists of two consecutive 1’s The AT LAN-
TIC Controller does not treat the SFD pattern as a byte it
detects only the two-bit pattern This allows any preceding
preamble within the SFD to be used for phase locking
Destination Address
The destination address indicates the destination of the
packet on the network and is used to filter unwanted pack-
ets from reaching a node There are three types of address
formats supported by the AT LANTIC physical multicast
and broadcast The physical address is a unique address
that corresponds only to a single node All physical address-
es have an MSB of ‘‘0’’ These addresses are compared to
the internally stored physical address registers Each bit in
the destination address must match in order for the
AT LANTIC Controller to accept the packet Multicast ad-
dresses begin with an MSB of ‘‘1’’ The AT LANTIC Con-
troller filters multicast addresses using a standard hashing
algorithm that maps all multicast addresses into a 6-bit val-
ue This 6-bit value indexes a 64-bit array that filters the
value If the address consists of all 1’s it is a broadcast
address indicating that the packet is intended for all nodes
A promiscuous mode allows reception of all packets the
destination address is not required to match any filters
Physical broadcast multicast and promiscuous address
modes can be selected
Source Address
The source address is the physical address of the node that
sent the packet Source addresses cannot be multicast or
broadcast addresses This field is simply passed to buffer
memory
Length Field
The 2-byte length field indicates the number of bytes that
are contained in the data field of the packet This field is not
interpreted by the AT LANTIC Controller
Data Field
The data field consists of anywhere from 46 to 1500 bytes
Messages longer than 1500 bytes need to be broken into
multiple packets Messages shorter than 46 bytes will re-
quire appending a pad to bring the data field to the minimum
length of 46 bytes If the data field is padded the number of
valid data bytes is indicated in the length field The
AT LANTIC Controller does not strip or append pad
bytes for short packets or check for oversize packets
FCS Field
The Frame Check Sequence (FCS) is a 32-bit CRC field
calculated and appended to a packet during transmission to
allow detection of errors when a packet is received During
reception error free packets result in a specific pattern in