DP83261 datasheet(98/132 Pages) NSC

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70 Signal Descriptions (Continued)

7433 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 ClaimBeacon 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 e 0) or lost

(TXABORT e 1) the Claim or Beacon process

The interpretation of TXED and TXABORT is given in Table

7-5

TABLE 7-5 Transmission Status

TXED

TXABORT

Condition

After a Master Reset or frame

aborted during successful

immediate Claim or Beacon

service due to My

Claim or

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

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

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

744 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 743 (

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

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

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