dp83261 National Semiconductor Corporation, dp83261 Datasheet - Page 5

• Manufacturer Part Number: dp83261
• Description: Bmac Device Fddi Media Access Controller
• Manufacturer: National Semiconductor Corporation

2 0 Architectural Description
2 1 RING ENGINE
The BMAC device is operated by the Ring Engine which is
comprised of four blocks Receiver Transmitter MAC Pa-
rameter RAM and Counters Timers as shown in Figure 2-2
2 1 1 Receiver
The Receiver Block accepts data from the PLAYER device
in the byte stream format (PH Indicate)
Upon receiving the data the Receiver Block performs the
following functions
And finally the Receiver Block presents the data to the
MAC Interface along with the appropriate control signals
(MA Indicate)
2 1 2 Transmitter
The Transmitter Block inserts frames from this station into
the ring in accordance with the FDDI Timed Token MAC
protocol It also repeats frames from other stations in the
ring The Transmitter block multiplexes data from the MA
Request Interface and data from the Receiver Block During
Frame Transmission data from the Request Interface is se-






Determines the beginning and ending of a Protocol Data
Unit (PDU)
Decodes the Frame Control field to determine the PDU
type (frame or token)
Compares the received Destination and Source Address-
es with the internal addresses
Processes data within the frame
Calculates and checks the Frame Check Sequence at
the end of the frame
Checks the Frame Status field
FIGURE 2-2 Ring Engine Overview Block Diagram
(Continued)
5
lected During Frame Repeating data from the Receiver
Block is selected
During Frame Transmission the Transmitter Block performs
the following functions
During Frame Repeating the Transmitter Block performs
the following functions
Whether transmitting or repeating frames the Transmitter
Block also performs the following functions
Data is presented from the Transmitter Block to the
PLAYER device in the byte stream format (PH Request)
2 1 3 MAC Parameter RAM
The MAC Parameter RAM block is a dual port RAM that
contains MAC parameters such as the station’s short and
long addresses These parameters are initiallzed via the
Control Interface Both the Receiver and Transmitter Blocks
may access the RAM








Captures a token to gain the right to transmit
Transmits one or more frames
Generates the Frame Check Sequence during transmis-
sion and appends it at the end of the frame
Generates the Frame Status field that is transmitted at
the end of the frame
Issues the token at the end of frame transmission
Repeats the received frame and modifies the Frame
Status field at the end of the frame as specified by the
standard
Strips the frame(s) that are transmitted by this station
Generates Idle symbols between frames
TL F 10387 – 4