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参数资料
| 型号： | AM79C965KCW |
| 厂商： | ADVANCED MICRO DEVICES INC |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 3 CHANNEL(S), LOCAL AREA NETWORK CONTROLLER, PQFP16 |
| 封装： | PLASTIC, QFP-160 |
| 文件页数： | 213/220页 |
| 文件大小： | 1197K |
| 代理商： | AM79C965KCW |
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AMD
P R E L I M I N A R Y
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Am79C965
be passed unmodified to the host. If the length field has
a value of 46 or greater, the MAC engine will not attempt
to validate the length against the number of bytes con-
tained in the message.
If the frame terminates or suffers a collision before 64
bytes of information (after SFD) have been received, the
MAC engine will automatically delete the frame from the
Receive FIFO, without host intervention.
Addressing (Source and Destination Address
Handling)
The first 6 bytes of information after SFD will be inter-
preted as the destination address field. The MAC engine
provides facilities for physical, logical (multicast) and
broadcast address reception. In addition, multiple physi-
cal addresses can be constructed (perfect address fil-
tering) using external logic in conjunction with the
EADI interface.
Error Detection (Physical Medium Transmission
Errors)
The MAC engine provides several facilities which report
and recover from errors on the medium. In addition, the
network is protected from gross errors due to inability of
the host to keep pace with the MAC engine activity.
On completion of transmission, the following transmit
status is available in the appropriate TMD and CSR
areas:
s The number of transmission retry attempts (ONE,
MORE or RTRY).
s Whether the MAC engine had to Defer (DEF) due to
channel activity.
s Excessive deferral (EXDEF), indicating that the
transmitter has experienced Excessive Deferral on
this transmit frame, where Excessive Deferral is de-
fined in ISO 8802-3 (IEEE/ANSI 802.3).
s Loss of Carrier (LCAR) indicates that there was an
interruption in the ability of the MAC engine to moni-
tor its own transmission. Repeated LCAR errors indi-
cate a potentially faulty transceiver or network
connection.
s Late Collision (LCOL) indicates that the transmission
suffered a collision after the slot time. This is indica-
tive of a badly configured network. Late collisions
should not occur in a normal operating network.
s Collision Error (CER) indicates that the transceiver
did not respond with an SQE Test message within
the predetermined time after a transmission com-
pleted. This may be due to a failed transceiver, dis-
connected or faulty transceiver drop cable, or the
fact the transceiver does not support this feature (or
it is disabled).
In addition to the reporting of network errors, the MAC
engine will also attempt to prevent the creation of any
network error due to the inability of the host to service
the MAC engine. During transmission, if the host fails to
keep the Transmit FIFO filled sufficiently, causing an
underflow, the MAC engine will guarantee the message
is either sent as a runt packet (which will be deleted by
the receiving station) or has an invalid FCS (which will
also cause the receiver to reject the message).
The status of each receive message is available in the
appropriate RMD and CSR areas. FCS and Framing er-
rors (FRAM) are reported, although the received frame
is still passed to the host. The error will only be reported
if an FCS error is detected and there are a non integral
number of bytes in the message. The MAC engine will
ignore up to 7 additional bits at the end of a message
(dribbling bits), which can occur under normal network
operating conditions. The reception of 8 additional bits
will cause the MAC engine to de-serialize the entire
byte, and will result in the received message and FCS
being modified.
The PCnet-32 controller can handle up to 7 dribbling bits
when a received frame terminates. During the recep-
tion, the FCS is generated on every serial bit (including
the dribbling bits) coming from the cable, although the
internally saved FCS value is only updated on the eighth
bit (on each byte boundary). The framing error is re-
ported to the user as follows:
s If the number of dribbling bits are 1 to 7 and there is
no CRC (FCS) error, then there is no Framing error
(FRAM = 0).
s If the number of dribbling bits are 1 to 7 and there is a
CRC (FCS) error, then there is also a Framing error
(FRAM = 1).
s If the number of dribbling bits = 0, then there is no
Framing error. There may or may not be a CRC
(FCS) error.
Counters are provided to report the Receive Collision
Count and Runt Packet Count for network statistics and
utilization calculations.
Note that if the MAC engine detects a received frame
which has a 00b pattern in the preamble (after the first
8-bits which are ignored), the entire frame will be ig-
nored. The MAC engine will wait for the network to go
inactive before attempting to receive additional frames.
Media Access Management
The basic requirement for all stations on the network is
to
provide
fairness
of
channel
allocation.
The
802.3/Ethernet protocols define a media access mecha-
nism which permits all stations to access the channel
with equality. Any node can attempt to contend for the
channel by waiting for a predetermined time (Inter Pack-
et Gap internal) after the last activity, before transmitting
on the media. The channel is a multidrop communica-
tions media (with various topological configurations per-
mitted) which allows a single station to transmit and all
other stations to receive. If two nodes simultaneously
contend for the channel, their signals will interact caus-
ing loss of data, defined as a collision. It is the responsi-
bility of the MAC to attempt to avoid and recover from a
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