DP83907VF National Semiconductor, DP83907VF Datasheet - Page 40

• Manufacturer Part Number: DP83907VF
• Description: IC CONTROLLR AT/LANII TP 160PQFP
• Manufacturer: National Semiconductor

Specifications of DP83907VF

• Controller Type: Network Interface Controller (NIC)
• Interface: Twisted Pair
• Voltage - Supply: 4.75 V ~ 5.25 V
• Current - Supply: 150mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 160-MQFP, 160-PQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *DP83907VF

5 0 Register Descriptions
tem designer would use a program to determine which filter
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 perfect filtering of
6 0 Operation of DP83907
This section details the operation of the DP83907 The op-
erations discussed are packet reception and transmission
bus operations and loopback diagnostics
6 1 TRANSMIT RECEIVE PACKET ENCAPSULATION
DECAPSULATION
A standard lEEE 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 DP83907 generates
and appends the preamble SFD and FCS field during trans-
mission The Preamble and SFD fields are stripped during
reception (The CRC is passed through to buffer memory
during reception )
multicast address it will perfectly filter up to 64 multicast addresses if
these addresses are chosen to map into unique locations in the multi-
cast filter
FIGURE 25 Multlcast Addressing
FIGURE 26 Ethernet Packet
(Continued)
TL F 12082–20
TL F 12082–21
40
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
DP83907 does not treat the SFD pattern as a byte it de-
tects 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 DP83907 physical multicast and
broadcast The physical address is a unique address that
corresponds only to a single node All physical addresses
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 DP83907 to
accept the packet Multicast addresses begin with an MSB
of ‘‘1’’ The DP83907 filters multicast addresses using a
standard hashing algorithm that maps all multicast address-
es into a 6-bit value 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 pack-
ets the destination address is not required to match any
filters Physical broadcast multicast and promiscuous ad-
dress 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 DP83907
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
DP83907 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
the CRC generator Packets with improper CRC will be re-
jected The AUTODIN II (X
X
polynomial is used for the CRC calculations
12
a
X
11
a
X
10
a
X
8
a
32
X
7
a
a
X
26
X
5
a
a
X
X
23
4
a
a
X
X
2
22
a
a
X
1
X
16
a
The
a
1)