參數(shù)資料
型號(hào)： MB86976PF-G
元件分類： 微控制器/微處理器
英文描述： 2 CHANNEL(S), 10M bps, LOCAL AREA NETWORK CONTROLLER, PQFP144
封裝： PLASTIC, QFP-144
文件頁(yè)數(shù)： 15/46頁(yè)
文件大小： 212K
代理商： MB86976PF-G
xDSL WAN Ethernet Bridge Controller
22
Fujitsu Microelectronics, Inc.
Advanced 11/5/98
WAN Filtering
Frames received from the WAN receive port are filtered with
respect to the contents of the protocol field. This is in addition to
and does not replace the frame validity checks performed by the
WAN Interface module, i.e. CRC verification.
Protocol Field
When the WAN is in modes HDLC, PPP or PPP-LEX, the
protocol field of frames received from the WAN receive port is used
to determine the destination of the frame. Based on the value, the
frame may be forwarded to the processor, LAN transmit port, or
both. Protocol values come in three ranges and indicate the type of
message being received:
Encapsulated data messages have a protocol field value between
0000h and 3FFFh, Network Control Protocol messages have a
protocol field value between 8000h and BFFFh, and Link Control
Protocol messages have a protocol field value between C000h and
FFFFh.
Due to the unique range of values, only the most significant bit of
the protocol field requires checking. If the protocol field MSB
value is 0, the frame contains an encapsulated data message and is
forwarded to the next stage of processing. If it is 1, the frame
contains either a Network Control Protocol (NCP) or Link
Control Protocol (LCP) message, and is written to the processor
frame buffer as well as the LAN.
Encapsulated Data Messages
When new frames received from the WAN receive port are
identified as encapsulated data messages, the following steps are
performed:
1.
A 10-bit hash value is calculated from the 48-bit Destination
Address and is used as the pointer to one of 1024 Source Address
database “buckets”.
2.
The corresponding “bucket” is linearly searched until a valid
entry containing an identical 48-bit address is found or the end of
the “bucket” is reached.
3.
If a valid matching entry is found and the Destination field is set
to “000”, then the frame is forwarded to the LAN port.
If a valid matching entry is found and the Destination field is set to
“001”, then the frame is forwarded to the processor.
If a valid matching entry is found and the Destination field is set to
“101”, then the frame is forwarded to both the LAN transmit
port and the processor.
If no valid matching entry is found, the frame is forwarded to the
LAN transmit port by default.
Network Control Protocol (NCP) and Link Control Protocol
(LCP) Messages
All frames received from the WAN receive port identified as either a
NCP or LCP message are unconditionally forwarded to the
processor.
Processor Filtering Statistics
Filtering statistics are available for maintenance and performance
monitoring. These are listed under the section headed Functional
Control and Status Register.
System Features
In addition to the signals associated with the varous interfaces,
clock and reset signals are provided, as well as LED outputs for
diagnostics.
Clocks
The MB86976 is operated by a single system clock running at
40 MHz. This is sufficient to perform all processing functions for
memory and filtering operations. It can recover off-chip input
signals up to a 20 MHz frequency.
The only other clock domain on the MB86976 is wholly contained
within the LAN MAC, which uses the transmit and receive clocks
from the external transceiver for part of its operation. These clock
domains are entirely isolated from the remainder of the MB86976,
and all system functions that access the MAC do so in the 40 MHz
system clock domain.
LED Outputs
The MB86976 provides seven status outputs intended to drive
system diagnostic LEDs.
The MB86976 imports the Carrier Sense and Collision Detect
signals from outputs generated by the external Ethernet
transceiver, e.g., the Fujitsu MB86961A. The other status LEDs
are generated by on-chip monitoring logic. Each LED output is
pulse stretched such that the minimum assertion time for any of the
LEDs is 25 ms, and will sink up to 12 mA.
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