dp83261 National Semiconductor Corporation, dp83261 Datasheet - Page 98

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

7 0 Signal Descriptions
7 4 3 3 Transmission Status
Upon leaving MR2 transmission status is available after
TXRDY or TXPASS is asserted TXED and TXABORT are
normally valid for at least 9 byte times (exception 2 byte
times when an Immediate Service Opportunity ends without
issuing a token and another Service Opportunity begins im-
mediately upon return to state MR0) THTDIS is valid for at
least 2 byte times When TXPASS is deasserted and for at
least two byte times after is reasserted TXCLASS denotes
the token that will be issued at the end of the current Serv-
ice Opportunity
TXED indicates that the Ending Delimiter of the previous
PDU was transmitted TXABORT indicates that the previous
frame was aborted as a result of a request abort (RQABT)
an internal error or the Reset or Recovery Required condi-
tions became true
If TXED is asserted TXABORT may also be asserted (within
9 byte clocks) if this station backed off to another station
after a complete Claim frame was transmitted
When transmitting Claim Beacon frames from the Transmit-
ter Claim or Beacon if TXPASS is asserted the Claim or
Beacon Process has completed In this case TXABORT
indicates if this station won (TXABORT
(TXABORT
The interpretation of TXED and TXABORT is given in Table
7-5
If TXPASS is asserted and THT was disabled during the last
frame that was transmitted (THTDIS is asserted) TRT has
expired This is a serious error and indicates that there was
TXED
0
1
0
1
TXABORT
e
TABLE 7-5 Transmission Status
1) the Claim or Beacon process
0
0
1
1
After a Master Reset or frame
aborted during successful
immediate Claim or Beacon
service due to My Claim or
My Beacon
Complete frame transmitted
Frame aborted
Complete frame transmitted
followed by reset or recovery
actions or unsuccessful immediate
Claim or Beacon service due to
timeout
Condition
(Continued)
e
0) or lost
98
an over-allocation of synchronous bandwidth or a station
used more than it was allocated The ring will likely be claim-
ing when this occurs
7 4 4 Timing Examples
Several example sequences of the MAC Request Interface
are provided While this in no way is an exhaustive list of
sequences several likely sequences are shown It is useful
to follow the state diagrams of Section 7 4 3 ( Figures 7-11
and 7-12 ) while examining the scenarios
The timing is shown for all signals available at the MAC
Interface
The data shown in MRD and PRD are the data at those
interfaces
The data at PRD is duplicated with the TXED to show its
relationship with the transmitted Ending Delimiter
TXPASS and TXRDY show the relationship to the data at
the transmitter This is one byte time before the data is
transmitted The relationship to incoming tokens is shown
explicitly
RQRCLS contains the Requested service class In several
examples this is shown as generic requests (r1 r2) to make
the examples more general purpose The RQCLM and
RQBCN signals are not shown but have the same timing as
the RQRCLS signals
The Frame Options are grouped together since they have
the same timing These include the SAT SAIGT FCST and
STRIP options
Single Frame Transmission with Prestaging
Prestaging refers to the staging of data before the Service
Opportunity begins Prestaging occurs in interfaces where
data is loaded into a FIFO or dedicated memory used as a
FIFO before the token arrives
In Figure 7-13 RQRDY is asserted one byte time after
RQRCLS has been passed to the interface At this point the
Ring Engine is awaiting an appropriate Service Opportunity
Upon capture of a usable token TXRDY is asserted
TXRDY causes RQSEND to be asserted
RQSEND causes TXRDY to be deasserted which in turn
causes RQSEND to be deasserted
Notice that after RQSEND is deasserted RQFINAL is as-
serted for one cycle to indicate that the issue token class
should be used for the token RQRDY is then deasserted
and RQRCLS is set to zero Since RQRCLS goes to zero
the end of Service Opportunity condition becomes true and
the token is issued at the end of the current frame