dp83261 National Semiconductor Corporation, dp83261 Datasheet - Page 17

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

5 0 Functional Description
Note 1 Synchronous Requests are not serviced when bit BCNR of the Ring Event Latch Register is set
Note 2 Restricted Requests are not serviced when bit BCNR CLMR or OTRMAC of the Ring Event Latch Register is set
Note 3 Restricted Dialogues only begin when a Non-Restricted token has been received and transmitted
Note 4 Immediate Requests are serviced when the ring is Non-Operational These requests are serviced from the Data state if neither signal RQCLM nor RQBCN
is asserted If signal RQCLM is asserted Immediate Requests are serviced from the Claim State If signal RQBCN is asserted Immediate Requests are serviced
from the Beacon State RQCLM and RQBCN do not cause transitions to the Claim and Beacon States
Requests are serviced on a Service Opportunity meeting
the requested criteria
External support is required to limit the requests presented
to the MAC Interface by different MAC Users (SMT LLC
etc )
A Token Capture Class of non-rstr indicates that the Trans-
mitter Token Class must be Non-Restricted to begin servic-
ing the request A Token Capture Class of rstr indicates
that the Transmitter Token Class must be Restricted to be-
gin servicing the Request A Token Issue Class of non-rstr
means that the Transmitter Token Class will be Non-Re-
stricted upon completion of the request A Token Issue
Class of rstr means that the Transmitter Token Class will be
Restricted upon completion of the request
5 3 2 Request Options
The Request Options provide the ability for Source Address
Transparency (SAT) and FCS Transparency (FCST) In both
cases data from the request stream is transmitted in place
of data from either the Ring Engine The use of Source Ad-
dress transparency has no effect on the sequencing of the
interface When Source Address transparency is not used
the SA from the internal parameter RAM is substituted for
the SA bytes in the request stream which must still be pres-
ent Since the FCS is appended to the frame when FCS
transparency is not used no FCS bytes are present in the
request stream
RQRCLS
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Reserved
Reserved
RbeginD
Apri 1
AsynD
Name
RcntD
ImmN
ImmR
RenD
None
Rbeg
Rend
Asyn
Rcnt
Imm
Syn
Immediate
Immediate
Immediate
Restricted
Restricted
Restricted
Restricted
Restricted
Restricted
Reserved
Reserved
Asynch
Asynch
THSH1
Async
Synch
Class
None
TABLE 5-3 Request Service Classes
(Continued)
Disabled
Disabled
Disabled
Disabled
Disabled
Disabled
Disabled
Disabled
Enabled
Enabled
Enabled
Enabled
Enabled
17
THT
Source Address Transparency
Normally the SA field in a frame is generated by the BMAC
device using either the MSA or MLA When the SA Trans-
parency option is selected the SA from the data stream is
transmitted in place of the MSA or MLA The SAT option
can be invoked on a per frame basis upon the assertion of
the SAT signal (Pin 12)
When the SA Transparency option is selected it is neces-
sary to rely on an alternate stripping mechanism because
stripping based on the returning SA only guarantees that
frames with MSA or MLA will be stripped Either the Void
Stripping option (described below) may be invoked or exter-
nal hardware that forces stripping using the EM (External
M Flag) signal is required
The MSB of the SA is not controlled by this option It is
normally forced to Zero It can be controlled using the
Source Address MSB Transparency option described be-
low
SA Transparency is possible for all frames (including MAC
frames) External support is required to limit the use of SA
Transparency to certain MAC Users SA Transparency
should not be used with externally generated MAC Frames
in order to maintain accountability but this is not enforced
by the Ring Engine
Capture
Non-rstr
Non-rstr
Non-rstr
Non-rstr
Non-rstr
Token
None
None
None
Any
Rstr
Rstr
Rstr
Rstr
Captured
Non-rstr
Non-rstr
Non-rstr
Non-rstr
Non-rstr
Non-rstr
Token
Issue
None
Rstr
Rstr
Rstr
Rstr
Rstr
Notes
2 3
2 3
1
4
4
4
2
2
2
2