DP8496 datasheet(44/92 Pages) NSC

44 / 92 page

40 Functional Description (Continued)

All the normal interrupts will be generated during the data

transfer phase of the command (Block Transfer Complete

Group Transfer Complete etc) In addition a ‘‘Group Com-

plete’’ interrupt will always be generated just before the Dis-

connect operation begins This will allow the processor to

process the information read from the SCSI bus while the

disconnect operation is taking place

ReselectSend DataDisconnect

(Opcode e 18h)

This combination command is identical to issuing the Rese-

lect command (10h) followed by a single byte Message In

phase using the Identify register contents followed by the

Send Data command (0Bh) followed by the Send Discon-

nect command (33h)

A ‘‘Group Complete’’ interrupt will always be generated just

before the Disconnect operation begins This will allow the

processor to set up the SCSI Bus Controller for a new com-

mand while the disconnect operation is taking place

ReselectReceive DataEnd (Opcode e 1Dh)

This combination command is identical to issuing the Rese-

lect command (10h) followed by a single byte Message In

phase using the Identify register contents followed by the

Receive Data command (3Fh) followed by the Send End

command (31h)

A ‘‘Group Complete’’ interrupt will always be generated just

before the Disconnect operation begins This will allow the

processor to process the information read from the SCSI

bus while the disconnect operation is taking place

ReselectSend DataEnd (Opcode e 19h)

This combination command is identical to issuing the Rese-

lect command (10h) followed by a single byte Message In

phase using the Identify register contents followed by the

Send Data command (0Bh) followed by the Send End com-

mand (31h)

A ‘‘Group Complete’’ interrupt will always be generated just

before the Disconnect operation begins This will allow the

processor to set up the SCSI Bus Controller for a new com-

mand while the disconnect operation is taking place

Wait-for-SelectReceive Command

(Opcode e 36h)

This command should normally be issued any time there is

no other SCSI bus data transfers in progress This will allow

new SCSI commands to be received by the DP84967 (con-

figured as a target)

The DP84967 will wait until it recognizes itself being select-

ed with BSY deasserted SEL asserted and its own ID pres-

ent on the SCSI data bus If the ATN signal was also assert-

ed a Message Out phase will be generated with an Identify

Message The Identify byte will be loaded into the Identify

serted the Command Phase will be entered immediately

without a Message Out phase

If a Message Out phase is executing and the ATN signal

remains asserted when the ACK signal is deasserted the

command is terminated with an ‘‘Uncompleted Command’’

interrupt This indicates that the Initiator is sending an ex-

tended or multi-byte message

After the first byte of the Command Phase has been read

from the SCSI bus the DP84967 will interpret the Group

Number in bits 5 6 and 7 This determines the total number

of bytes in the SCSI Command Descriptor Block as shown

in Table 421 The correct number of bytes are then read

from the SCSI bus The entire SCSI Command Descriptor

Block will be transferred to buffer memory

TABLE 421 Group Numbers

Group Number

of Bytes in

Command

000

001

010

101

Note

Any other group combinations are unknown length and will cause an

‘‘Uncompleted Command’’ interrupt

A SCSI bus parity error or the assertion of the ATN signal

will terminate this command The termination will occur im-

mediately or at the end of the current phase based on the

SE (Stop Enable) bit in the SCSI Operation register Also

during a Message Out phase if the ATN signal goes low

the command will terminate based on the SE bit

The command will terminate after the last Command De-

scriptor byte has been read An ‘‘Operation Complete’’ in-

terrupt will be generated The SCSI Control signals will re-

main in the Command Phase

The Clear Pending Command can be issued to terminate

this command if the DP84967 has not yet been selected

If the DP84967 is reselected as an Initiator (before it has

been selected as a Target) the chip will respond properly

as an Initiator on the SCSI bus as if there were no active

command The Wait-for-SelectReceive command will then

terminate with a ‘‘(Re)Selected’’ interrupt and the ‘‘Last

Command Ignored’’ bit set also

Wait-for-SelectReceive CommandDisconnect

(Op-Code e 37h)

This command is identical to the previous command except

with the addition of an optional Disconnect function at the

end

If the SCSI Command Descriptor Block that is read from the

SCSI bus is a read disk command the DP84967 will enter

the ‘‘Message In’’ phase send a ‘‘Disconnect’’ message

and terminate with an ‘‘Operation Complete’’ interrupt A

read command is determined by the first byte of the Com-

mand Descriptor Block that was transferred during the Com-

mand Phase If this byte is either a 08h 28h 48h or A8h

then this is interpreted as a read command

If it is not a read command the command will terminate

after the last Command Descriptor byte has been read An

‘‘Uncompleted Command’’ interrupt will be generated In

this case the SCSI Control signals may not remain in the

Command Phase

Wait-for-SelectSend Busy (Opcode e 35h)

If no command can be accepted by the Target this com-

mand will turn away all Selections in a clean manner with

minimal processor overhead This command operates the

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