DP8496 datasheet(42/92 Pages) NSC

42 / 92 page

40 Functional Description (Continued)

Reset (Opcode e 2B)

This command will terminate and clear the current com-

mand (if any) and will clear any pipelined command Refer

to Table 31 for other registers that are affected by this com-

mand This command may be issued at any time

At the completion of this command the ‘‘Operation Com-

plete’’ interrupt will be generated This interrupt may be buff-

ered after another interrupt as described in the SCSI Inter-

rupt register

Disconnect (Opcode e 32h)

This command will immediately release the SCSI lines to

the Bus Free phase This command must be issued only if

there are no pending commands (Status Code in SCSI

Status register e 0111)

This command will not generate an interrupt because it is

immediate without the possibility of an error

Message Accepted (Opcode e 30h)

Valid only as an initiator This command should be used

after a Transfer Info or Transfer Pad command while in the

Message In phase At the termination of the Transfer Info or

Transfer Pad command the ACK signal will normally be

deasserted However if these commands are issued while

in the Message In phase the ACK signal will remain assert-

ed at the termination of the command The Message Ac-

cepted command can be used to deassert the ACK signal in

this case

If the message is to be accepted issue the Message Ac-

cepted command which will deassert the ACK signal If the

message is to be rejected the ATN signal should be assert-

ed before the Message Accepted command is issued The

ATN signal may be asserted by setting the ATN bit in the

SCSI Control register

(Re)Select (Opcode e 10h)

This command initiates a rather lengthy series of events

commencing with detecting the Bus Free phase An Arbitra-

tion phase is executed next if enabled in the SCSI Operation

Setup 2 register) on the SCSI bus and detects if any device

of higher priority is arbitrating with it The DP84967 will

cycle through this sequence until it wins arbitration After

winning arbitration the chip Selects the Target or Reselects

the Initiator whose ID is contained in the Destination ID reg-

ister It will wait for a response from that device indefinitely

with SEL and ID’s asserted and BSY deasserted When the

selected device responds by asserting BSY the command

will terminate with a completion interrupt

None of the above sequences are protected by time-outs

because it is much more efficient to bracket the entire se-

lection process with a single processor controlled timer

The choice between Selection and Reselection is deter-

mined by the TI (TargetInitiator) bit in the SCSI Operation

cute a Reselection While in the Initiator mode a Selection

will be executed

While in the Initiator mode the ATN signal may be con-

trolled during selection by the SWA (Select With Attention)

bit in the SCSI Operation register

Abort (Re)Selection (Opcode e 08h)

This command is used to terminate a pending (Re)select

combination command This command will function correct-

ly only if the initial (re)selection has not yet begun or while

the (re)selection is in progress

If this command is issued before or during arbitration the

SCSI bus is immediately released This will result in an ‘‘Op-

eration Complete’’ interrupt

If issued after this point but before the desired SCSI device

has responded with the BSY signal the SCSI Data Bus will

be released If the BSY signal is not detected after a certain

delay the SEL signal will be deasserted and the command

will terminate with an ‘‘Operation Complete’’ interrupt If the

BSY signal is detected a ‘‘Last Command Ignored’’ inter-

rupt will be generated and the DP84967 will continue as if

the Abort (Re)Selection command had not been issued at

all (except for the ‘‘Last Command Ignored’’ interrupt) This

follows option 2 of paragraph 5135 of the X3131-1986

specification

If this command is issued after the desired SCSI device has

already responded with the BSY signal no interrupt will be

generated for this command The DP84967 will continue

as if the Abort (Re)Selection command had not been issued

at all

To verify the result of this command the SCSI Status regis-

ter should be read at least 20 BCLK periods after this com-

mand is issued If the Status Code is less than 7 (0000 –

0111) the Abort (Re)Select command was issued in time

Simply wait for the completion interrupt

If the Status Code is 7 or greater (0111 – 1111) the Abort

(Re)Select command was issued too late The Selection

has already completed and there may be no completion

interrupt generated by the Abort (Re)Selection command

However a completion interrupt will be generated when the

original (Re)Select or (Re)Select combination command ter-

minates

Receive Command (Opcode e 3Eh)

Receive Data (Opcode e 3Fh)

Receive Message (Opcode e 3Ah)

Receive Unspecified (Opcode e 3Bh)

Send Status (Opcode e 0Ah)

Send Data (Opcode e 0Bh)

Send Message (Opcode e 0Eh)

Send Unspecified (Opcode e 0F)

The Send and Receive commands listed above are used to

transfer information on the SCSI bus The information trans-

ferred will be to or from the buffer memory

These commands are only valid if the DP84967 is config-

ured as a Target in the Automatic mode The DP84967

must already be connected (BSY asserted) The function of

these commands are all similar except for the IO CD and

MSG lines The state of these control lines are listed in

Table 420

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