dp83261 National Semiconductor Corporation, dp83261 Datasheet - Page 7

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

3 0 Feature Overview
3 1 FDDI MAC SUPPORT
The BMAC device implements the Standard ANSI X3T9 5
FDDI MAC protocol for transmitting receiving repeating
and stripping frames Many of the capabilities defined in
MAC-2 are included in the BMAC device such as bridging
end station support for setting the control indicators and
the statistic counters The BMAC device provides all of the
information necessary to implement the service primitives
defined in the standard
The BMAC device also implements many of the permitted
extensions to the FDDI-MAC standard as captured in the
FDDI MAC-2 document These include the extensions for
MAC level bridging Group Addressing support that can be
used for SMT reporting of additional events to aid the ring
management processes and enhanced versions of the state
machines
3 2 MAC ADDRESSING SUPPORT
Both long (48-bit) and short (16-bit) addressing are support-
ed simultaneously for both Individual and Group addresses
Up to 128 contiguous programmable group addresses and
up to 15 Fixed Group Addresses plus the universal broad-
cast address are recognized Limited operation with null ad-
dresses is supported An interface to external address
matching logic is provided to augment the Ring Engine’s
addressing capabilities
3 3 MAC BRIDGING SUPPORT
Several features are provided to aid in Bridging applications
On the receive side external address matching logic can be
used to examine the PH Indicate byte stream to decide
whether to copy a frame how to set the control indicators
and how to increment the counters
On the transmit side transparency options are provided on
the Source Address the most significant bit of the Source
Address and the FCS
In addition support for an alternate Void stripping mecha-
nism provides maximal flexibility in the generation of frames
3 4 MAC SERVICE CLASS SUPPORT
All of the FDDI MAC service classes are supported by the
BMAC device These include the Synchronous Asynchro-
nous Restricted Asynchronous and Immediate service
classes
For Synchronous transmission one or more frames are
transmitted in accordance with the station’s synchronous
bandwidth allocation
For Asynchronous transmission one programmable asyn-
chronous priority threshold is supported in addition to the
threshold at the Negotiated Target Token Rotation time
For Restricted Asynchronous transmission support is pro-
vided to begin continue and end restricted dialogues
For Immediate transmissions support is provided to send
frames from either the Data Beacon or Claim states and
either ignore or respond to the received byte stream After
an immediate transmission a token may optionally be is-
sued
3 5 DIAGNOSTIC COUNTERS
The BMAC device includes a number of diagnostic counters
that monitor ring and station performance
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7
These counters allow measurement of the following
The size of these counters has been selected to keep the
frequency of overflow small even under worst case operat-
ing conditions
3 6 MANAGEMENT SERVICES
The BMAC device provides management services to the
Host System via the Control Bus Interface This interface
allows access to internal registers to control and configure
the BMAC device
3 7 RING PARAMETER TUNING
The BMAC device includes settable parameters to allow
tuning of the network to increase performance over a large
range of network sizes
The BMAC device supports systems of two stations with
little cable between them to ring configurations much larger
than the 1000 physical attachments and or 200 km dis-
tance that are specified as the default values in the stan-
dard
The BMAC device also handles frames larger than the 4500
byte default maximum frame size as specified in the Stan-
dard
3 8 MULTI-FRAME STREAMING INTERFACE
The BMAC device provides an interface to support a multi-
frame streaming interface Multiple frames can be transmit-
ted after a token is captured within the limits of the token
timer thresholds
3 9 GENERATES BEACON CLAIM
AND VOID FRAMES INTERNALLY
For purposes of transient token and ring recovery no proc-
essor intervention is required The BMAC device automati-
cally generates the appropriate MAC frames
3 10 SELF TESTING
Because the BMAC device is full duplex loopback testing is
possible before entering the ring and during normal ring op-
eration
There are several posible loopback paths
These paths allow error isolation down to the device level
The BMAC device also supports through parity









Number of frames transmitted and received by the sta-
tion
Number of frames copied as well as frames not copied
because of insufficient buffering
Frame error rate of an incoming physical connection to
the MAC
Load on the ring based on the number of tokens re-
ceived and the ring latency
Ring latency
Lost frames
internal to the BMAC device
through the PLAYER device(s) using the PLAYER device
configuration switch
through the CRD device