AM53CF94 datasheet(39/76 Pages) AMD

39 / 76 page

P R E L I M I N A R Y

AMD

Am53CF94/Am53CF96

Initiator Command Complete Steps

(Command Code 11H/91H)

The Initiator Command Complete Steps command is

normally issued when the SCSI bus is in the Status In

phase. One Status byte followed by one Message byte

is transferred if this command completes normally. After

receiving the message byte the device will keep the

ACK signal asserted to allow the Initiator to examine the

message and assert the

ATN signal if it is unacceptable.

The command terminates early if the Target does not

switch to the Message In phase or if the Target discon-

nects from the SCSI bus.

Message Accepted Command

(Command Code 12H)

The Message Accepted Command is used to release

the

ACK signal. This command is normally used to com-

plete a Message In handshake. Upon execution of this

command the device generates a service request inter-

rupt after

REQ is asserted by the Target.

After the device has received the last byte of message, it

keeps the

ACK signal asserted. This allows the device

to either accept or reject the message. To accept the

message, Message Accepted Command is issued. To

reject the message the

ATN signal must be asserted

(with the help of the Set

ATN Command) before issuing

the Message Accepted Command. In either case the

Message Accepted Command has to be issued to re-

lease the

ACK signal.

Transfer Pad Bytes Command

(Command Code 18H/98H)

The Transfer Pad Bytes Command is used to recover

from an error condition. This command is similar to the

Information Transfer Command, only the information

bytes consists of null data. It is used when the Target ex-

pects more data bytes than the Initiator has to send. It is

also used when the Initiator receives more information

than expected from the Target.

When sending data to the SCSI bus, the FIFO is loaded

with null bytes which are sent out to the SCSI bus. Al-

though an actual DMA request is not made, DMA must

be enabled when pad bytes are transmitted since the

ESC uses Current Transfer Count Register (CTCREG)

to terminate transmission.

When receiving data from the SCSI bus, the device will

receive the pad bytes and place them on the top of the

FIFO and unload them from the bottom of the FIFO.

This command terminates under the same conditions as

the Information Transfer Command, but the device does

not keep the

ACK signal asserted during the last byte of

the Message In phase. Should this command terminate

prematurely due to a disconnect or a phase change,

(before the Current Transfer Count Register (CTCREG)

decrements to zero), the FIFO may contain residual pad

bytes.

Set ATN Command (Command Code 1AH)

The Set

ATN Command is used to drive the ATN signal

active on the SCSI bus. An interrupt is not generated at

the end of this command. The

ATN signal is deasserted

before asserting the

ACK signal during the last byte of

the Message Out phase.

Note:

The

ATN signal is asserted by the device without this

command in the following cases:

s If any select with

ATN command is issued and the

arbitration is won.

s An Initiator needs the Target’s attention to send a

message. The

ATN signal is asserted before

deasserting the

ACK signal.

Reset ATN Command (Command Code 1BH)

The Reset

ATN Command is used to deassert the ATN

signal on the SCSI bus. An interrupt is not generated at

the end of this command. This command is used only

when interfacing with devices that do not support the

Common Command Set (CCS). These older devices do

not deassert their

ATN signal automatically on the last

byte of the Message Out phase. This device does deas-

sert its

ATN signal automatically on the last byte of the

Message Out phase.

Target Commands

Target commands are executed by the device when it is

in the Target mode. If the device is not in the Target

mode and a Target command is received the device will

ignore the command, generate an Invalid Command in-

terrupt and clear the Command Register (CMDREG).

A SCSI bus reset during any Target command will cause

the device to abort the command sequence , flag a SCSI

bus reset interrupt (if the interrupt is enabled) and dis-

connect from the SCSI bus.

Normal or successful completion of a Target command

will cause a Successful Operation interrupt to be

flagged. If the

ATN signal is asserted during a Target

command sequence the Service Request bit is asserted

in the Interrupt Status Register (INSTREG). If the

ATN

signal is asserted when the device is in an Idle state a

Service Request interrupt will be generated, the Suc-

cessful Operation bit in the Interrupt Status Register

(INSTREG) will be reset and the Command Register

(CMDREG) cleared.

Send Message Command

(Command Code 20H/A0H)

The Send Message Command is used by the Target to

inform the Initiator to receive a message. The SCSI bus

phase lines are set to the Message In Phase and mes-

sage bytes are transferred from the device FIFO to the

buffer memory.

Send Status Command

(Command Code 21H/A1H)

The Send Status Command is used by the Target to in-

form the Initiator to receive status information. The SCSI

bus phase lines are set to the Status Phase and status

bytes are transferred from the Target device to the Initia-

tor device.

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