DP8496 datasheet(41/92 Pages) NSC

41 / 92 page

40 Functional Description (Continued)

The valid SCSI Commands are listed in Table 419 Flow-

charts of the multi-phase commands are shown in

Figures

412 to 419 at the end of this description of the SCMD

TABLE 419 SCSI Command Opcodes

Op-

Command

Mode

Int

Code

Clear Pending Command

Reset

Disconnect

Message Accepted

(Re)Select

Abort (Re)Select

Receive Command

Receive Data

Receive Message

Receive Unspecified

Send Status

Send Data

Send Message

Send Unspecified

Transfer Info

Transfer Pad

Send Disconnect

Send End

Reselect-Receive Data

Reselect-Send Data

Reselect-Receive Data-

Disconnect

Reselect-Send Data-

Disconnect

Reselect-Receive Data-End

Reselect-Send Data-End

Wait for Sel-Busy-End

Wait for Sel-Receive

Command

Wait for Sel-Receive

Command-Disconnect

(Re)Select Self Test

Disconnect Self Test

Send Data Loopback

Receive Data Loopback

Transfer Info Loopback

Mode I e Initiator T e Target

INT e Interrupt generated at command termination (YN)

Clear Pending Command (Opcode e 00)

This command will clear the SCSI Command register of any

outstanding or pending commands This may be used in the

following situations

1 After a ‘‘Wait for Select’’ command is written to the SCSI

Command register a Clear Pending Command may be

issued to prevent the ‘‘Wait for Select’’ command from

executing See Section 443 for a description of the

proper sequence to clear the ‘‘Wait for Select’’

2 If a new command is written to the SCSI Command regis-

ter and you want to prevent it from executing you may

issue the Clear Pending Command The following condi-

tion may create this situation

A If a command is pipelined the Clear Pending Com-

mand may be issued to clear the pipelined command

before it is executed See 443 for pipelining restric-

tions

B If a command is pipelined and the currently executing

command terminates with an error the pipelined

command will not execute until the interrupt is

cleared The Clear Pending Command may be issued

to clear the pipelined command before it is executed

C If an asynchronous event generates a completion in-

terrupt (SCSI Bus Reset or (Re)Select) just before a

command is written to the SCSI Command register

the command will be pipelined and will not execute

until the interrupt is cleared The Clear Pending Com-

mand may be issued to clear the pipelined command

before it is executed

3 Before modifying the TI (TargetInitiator) bit in the SCSI

Operation register the Clear Pending Command should

be issued This will prevent an ‘‘Invalid Command’’ inter-

rupt from being issued if the last command written to the

SCSI Command register is invalid for the new mode set

with the TI bit This operation is not required if you are

sure that the last command is not invalid for the new

mode

4 The Clear Pending Command is used to clear the self

test mode The Clear Pending Command should be is-

sued after issuing the Disconnect Self Test command

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