DP83261AVF datasheet(22/132 Pages) NSC

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50 Functional Description (Continued)

by setting bit FunctionBCN to One Entry to the Claim State

can be forced by setting bit FunctionCLM to One

While in the Claim or Beacon state the Ring Engine will

transmit internally generated Claim or Beacon frames ex-

cept when an Immediate Claim or Beacon request is pres-

ent at the MA

Request Interface

signal RQCLM or

RQBCN is asserted and a frame is ready to be transmitted

At least one internally generated Claim or Beacon frame

must be transmitted before an Immediate Claim or Beacon

request is serviced It is possible for the internally generated

frame to return before the end of the requested frame has

been transmitted To allow time for the requested frame(s)

to be transmitted before leaving the Claim or Beacon state

bit ITR (for Claim) or bit IRR (for Beacon) of the Option

While an Immediate request is being serviced (from any

state) if bit IRPT of the Option Register is set to One (Inhibit

Repeat option) all received frames (except Lower

Claim

and My

Beacon frames) are ignored and the Immediate

request continues Lower

Claim and My

Beacon frames

can also be ignored by setting bit IRR of the Option Regis-

ter

510 FULL DUPLEX OPERATION

The BMAC device supports full duplex operation by

1 Suspending the Token Management and Token Recov-

ery protocols (set OptionIRR)

2 Inhibiting the repetition of all PDUs (set OptionIRPT)

3 Using the Immediate Service Class

Frames of any size may be transmitted or received subject

to the minimum length specified in Section 54

511 PARITY PROCESSING

The BMAC device contains five data interfaces as shown in

Table 5-6

Through Parity is supported on the internal data paths be-

tween any Request interface and any Indicate interface

Odd Parity is provided every clock on all data outputs and is

checked every clock on all data inputs Parity errors are not

propagated through the BMAC device (from the MAC Re-

quest and PHY Indication interface to the PHY Request in-

terface or from the PHY Indication interface to the MAC

Indication interface) Parity errors are isolated and resolved

When parity is not used on an Interface the parity provided

by the BMAC device for its outputs may be ignored For the

BMAC device’s inputs the result of the parity check is used

only if parity on that Interface is enabled

Interface parity is enabled by setting the appropriate bit in

the Mode register ModeCBP for Control Bus Parity Mo-

dePIP for PHY Indication parity and ModeMRP for MAC

Request Parity A Master Reset (Function MARST) disables

parity on all interfaces

On the PHY Request interface parity is generated for inter-

nally sourced fields (such as the SA or FCS on frames when

not using SA or FCS transparency and internally generated

Beacon Claim and Void frames) In REV 1 of the BMAC

device MRP is passed transparently to PRP for externally

sourced fields independent of the value of the ModeMRP

In all later revisions correct Odd parity is always generated

for PRP This allows through parity support at the PHY inter-

face even if parity is not used at the MAC interface This is

very desirable since every byte of data that traverses the

ring travels across the PHY Interface which is actually part

of the ring

Through parity is not supported in the Control Interface Reg-

isters and the Parameter RAM Parity is generated and

stripped at the Control Interface

Handling Parity Errors

Parity errors are reported in the Exception Status Register

when parity on that interface is enabled

A parity error at the PHY interface (when ModePIP is set) is

treated as a code violation and ESRPPE is set If the parity

error occurs in the middle of a PDU (token or frame) recep-

tion

the PDU is stripped

a Format Error is signaled

(FOERROR) and the Lost Count is incremented

A parity error at the MAC Interface (when ModeMRP is set)

during a frame transmission from the MAC interface (while

TXACK is asserted) causes the frame transmission to be

aborted When a frame is aborted a Void frame is transmit-

ted to reset every station’s TVX timer A parity error (when

enabled) causes ESRMPE to be set

A parity error at the Control Interface (when ModeCBP is

set) will cancel the current write access ESRCPE is set to

indicate that a parity error occurred and ESRCCE is set to

indicate that the write was not performed

TABLE 5-6 BMAC Device Parity

Interface

Parity

Direction

MAC Request Interface

MRD(70)

MRP

MAC Indication Interface

MID(70)

MIP

PHY Request Interface

PRD(70)

PRP

PRC

PHY Indication Interface

PID(70)

PIP

PIC

Control Interface

CBD(70)

CBP

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