dp83261 National Semiconductor Corporation, dp83261 Datasheet - Page 4

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

Figure 2-1
2 0 Architectural Description
The BMAC device receivers transmits and strips or repeats
Protocol Data Units (PDUs i e Tokens and Frames) and
handles the token management functions required by the
timed token protocol in accordance with the FDDI MAC
Standard
The BMAC device is comprised of the Ring Engine (RE) and
interfaces to the Control Bus (Control Interface) the
PLAYER device (PHY Interface) and a System Interface
such as the BSI device (MAC Interface) as shown in
On transmission the system interface prepares one or more
frames for transmission and requests a service opportunity
Based on the requested service class and requested token
type the Ring Engine waits for a token meeting the request-
ed criteria When a token is captured the Ring Engine sig-
nals the interface and soon thereafter transmission begins
After traversing the ring frames are stripped based on the
FIGURE 2-1 BMAC Device Interfaces
4
Source Address Frames with a Source Address matching
one of the station individual addresses are stripped by the
Ring Engine Status is available at the MAC interface for
every transmitted frame
For reception the Ring Engine sequences through the in-
coming byte stream comparing received destination ad-
dresses against the station’s short or long address The re-
sults of these comparisons are made available at the MAC
interface The System Interface then decides how to handle
the frame In the normal case a frame with a Destination
Address matching one of the station addresses is copied
and passed to the system
The BMAC device utilizes a full duplex byte-wide (symbol
pair) architecture There are two bytes of delay in the Trans-
mit path three bytes of delay in Receive and Repeat paths
and two bytes of delay in the Loopback path
TL F 10387 – 2