AM53CF94JC datasheet(42/76 Pages) AMD

42 / 76 page

P R E L I M I N A R Y

AMD

Am53CF94/Am53CF96

Select without ATN Steps Command

(Command Code 41H/C1H)

The Select without

ATN Steps Command is used by the

Initiator to select a Target. When this command is

issued the device arbitrates for the control of the SCSI

bus. When the device wins arbitration, it selects the

Target device and transfers the Command Descriptor

Block (CDB). Before issuing this command the SCSI

Timeout Register (STIMREG), the Control Register

One (CNTLREG1) and the SCSI Destination ID Regis-

ter (SDIDREG) must be set to the proper values. If DMA

enabled,

the

Start

Transfer

Count

(STCREG) must be set to the total length of the

command. If DMA is not enabled, the data must be

loaded into the FIFO before issuing this command. This

command will be terminated early if the SCSI Timeout

Command Phase following the Selection Phase or if the

Target exits the Command Phase prematurely. A

Successful Operation interrupt will be generated follow-

ing normal command execution.

Select with ATN Steps Command

(Command Code 42H/C2H)

The Select with

ATN Steps Command is used by the In-

itiator to select a Target. When this command is issued

the device arbitrates for the control of the SCSI bus.

When the device wins arbitration, it selects the Target

device with the

ATN signal asserted and transfers the

Command Descriptor Block (CDB) and a one byte mes-

sage. Before issuing this command the SCSI Timeout

(CNTLREG1) and the SCSI Destination ID Register

(SDIDREG) must be set to the proper values. If DMA is

enabled, the Start Transfer Count Register (STCREG)

must be set to the total length of the command and mes-

sage. If DMA is not enabled, the data must be loaded

into the FIFO before issuing this command. This com-

mand will be terminated early in the following situations:

s The SCSI Timeout Register times out

s The Target does not go to the Message Out Phase

following the Selection Phase

s The Target exits the Message Phase early

s The Target does not go to the Command Phase

following the Message Out Phase

s The Target exits the Command Phase early

A Successful Operation/Service Request interrupt

is generated when this command is completed success-

fully.

Select with ATN and Stop Steps Command

(Command Code 43H/C3H)

The Select with

ATN and Stop Steps Command is used

by the Initiator to send messages with lengths other than

1 or 3 bytes. When this command is issued, the device

executes the Selection process, transfers the first mes-

sage byte, then STOPS the sequence.

ATN is not deas-

serted at this time, allowing the Initiator to send addi-

tional message bytes after the ID message. To send

these additional bytes, the Initiator must write the trans-

fer counter with the number of bytes which will follow,

then issue an information transfer command. (Note: the

Target is still in the message out phase when this com-

mand is issued).

ATN will remain asserted until the

transfer counter decrements to zero.

The SCSI Timeout Register (STIMREG), Control Regis-

ter One (CNTLREG1), and the SCSI Destination ID

before beginning the Initiator issues this command. This

command will be terminated early if the STIMREG times

out or if the Target does not go to the Message Out

Phase following the Selection Phase.

Enable Selection/Reselection Command

(Command Code 44H/C4H)

The Enable Selection/Reselection Command is used by

the Target to respond to a bus-initiated Selection or

Reselection. Upon disconnecting from the bus the Se-

lection/Reselection circuit is automatically disabled by

device. This circuit has to be enabled for the device to

respond to subsequent reselection attempts and the En-

able Selection/Reselection Command is issued to do

that. This command is normally issued within 250 ms

(select/reselect timeout) after the device disconnects

from the bus. If DMA is enabled the device loads the re-

ceived data to the buffer memory, but if the DMA is dis-

abled, the received data stays in the FIFO.

Disable Selection/Reselection Command

(Command Code 45H/C5H)

The Disable Selection/Reselection Command is used

by the Target to disable response to a bus-initiated

Reselection. When this command is issued before a bus

initiated Selection or Reselection is initiated, it resets

the internal mode bits previously set by the Enable Se-

lection/Reselection Command. The device also gener-

ates a function complete interrupt to the processor. If

however, this command is issued after a bus initiated

Selection/Reselection has already begun the command

is ignored since the Command Register (CMDREG) is

held reset and all incoming commands are ignored. The

device generates a selected or reselected interrupt

when the sequence is complete.

Select with ATN3 Steps Command

(Command Code 46H/C6H)

The Select with

ATN3 Steps Command is used by the

Initiator to select a Target. This command is similar to

the Select with

ATN Steps Command, except that it

sends exactly three message bytes. When this com-

mand is issued the ESC arbitrates for the control of the

SCSI bus. When the device wins arbitration, it selects

the Target device with the

ATN signal asserted and

transfers the Command Descriptor Block (CDB) and

three message bytes. Before issuing this command the

SCSI Timeout Register (STIMREG), the Control Regis-

ter One (CNTLREG1) and the SCSI Destination ID Reg-

ister (SDIDREG) must be set to the proper values. If

DMA is enabled, the Start Transfer Count Register

(STCREG) must be set to the total length of the com-

mand. If DMA is not enabled, the data must be loaded

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