DP83261AVF datasheet(97/132 Pages) NSC

97 / 132 page

70 Signal Descriptions (Continued)

SUBSTATE MRR0 Preamble

Upon entry to MR1 8 bytes of Preamble (Idles) are transmit-

ted in substate MRR0

After the Preamble if a frame can be sent from the inter-

face

transition MR12 occurs

The frame options are

latched TXED is cleared and TXACK is asserted

If a frame cannot be sent from the interface either Fill (addi-

tional Idles) or an internally generated frame (Void Claim or

Beacon) is transmitted

SUBSTATE MRR1 Fill

For requests if RQRDY is asserted (indicating that the cur-

rent request has been selected for service) or OptionIRPT

is set (indicating that the ring is being interrupted) additional

fill bytes (Idles) are transmitted in substate MRR1

Fill continues until

1) a frame can be sent from the interface or

2) the Service Opportunity ends or

3) 32 bytes of Idles are transmitted or RQRDY is deas-

serted After that an internal Void frame is generated

in substate MRR2 (If OptionIRPT is set Void frames

are not generated)

If RQRDY is not asserted if RQCLM or RQBCN is asserted

or (unless OptionIRPT is set) if the previous frame in the

current Service Opportunity was aborted an internal Void

Claim or Beacon frame is generated in substate MRR2

At the end of an internal frame TXED is set TXABORT is

cleared and another preamble is generated in substate

MRR0

MR2 Sending

In this state the Ring Engine is transmitting a frame from the

MAC Request Interface While the frame is being sent if an

unserviceable request is presented or any timer threshold is

reached the Service Opportunity will end after the current

frame

This implies that a Service Opportunity is never longer than

TMAX plus one maximum length frame interval for Immedi-

ate Requests (unless OptionIRPT is set) or TNEG plus one

maximum length frame interval for Non-immediate Re-

quests The maximum length of the frame interval is the

maximum send window open time (464 ms – 528 ms) plus

max F

max is the maximum length of a frame includ-

ing 2 bytes of Preamble The default value of F

max for

FDDI is 4500 bytes e 36000 ms

On entry to MR2 TXACK is asserted It remains asserted

while data is being accepted from the interface RQSEND

must be deasserted within one byte time after entering

MR2

At any time after RQSEND is deasserted for the final frame

of a request RQFINAL may be asserted to indicate that a

token of the Issue Token Class should be transmitted at the

end of the current Service Opportunity If the MR(20) tran-

sition occurs while RQFINAL is asserted and all the other

conditions for accepting RQFINAL hold the transmitted to-

ken will be the issue token class

After RQFINAL has been asserted no more frames can be

sent until RQRDY has been deasserted and then reassert-

ed RQRDY should be deasserted and the service parame-

ters updated to reflect the next requests (if any) as soon as

possible to allow the Ring Engine to make better ring

scheduling decisions

The last byte of data at the interface is indicated by RQEOF

which must be asserted with the last byte of data After the

Ending Delimiter of a frame is transmitted TXED is assert-

ed When not using FCS transparency TXED is asserted 7

byte times after RQEOF is asserted When using FCS trans-

parency it is asserted 3 byte times after RQEOF is assert-

ed TXACK is deasserted no later than one byte time after

RQEOF is asserted

At any time during frame transmission TXABORT may be

asserted This indicates that the frame was aborted due to

internal errors buffering errors parity errors RQABT MAC

reset reception of a MAC frame etc TXACK is deasserted

no later than TXABORT is asserted When a transmission is

aborted due to an error (and OptionIRPT is not set) a Void

frame is transmitted to reset the TVX timers in all stations in

the ring

After a successful or unsuccessful frame transmission if the

current Service Opportunity can be continued transition

MR(21) occurs and TXRDY is asserted otherwise transition

MR(20) occurs and TXPASS is asserted

If at any time during a frame transmission the end of Serv-

ice Opportunity condition is detected transition MR(20) will

occur after the current frame transition

DP83261AVF Datasheet(PDF) 97 Page - National Semiconductor (TI)

DP83261AVF Datasheet(HTML) 97 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL