AM53C96 datasheet(34/63 Pages) AMD

34 / 63 page

P R E L I M I N A R Y

AMD

Am53C94/Am53C96

COMMAND DESCRIPTION

Initiator Commands

Initiator commands are executed by the device when it

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

mode and an initiator command is received the device

will ignore the command, generate an illegal command

interrupt and clear the Command Register (CMDREG)

03H.

Information Transfer Command

(Command Code 10H/90H)

The Information Transfer command is used to transfer

information bytes over the SCSI bus. This command

may be issued during any SCSI Information Transfer

phase. Information transfer for synchronous data must

use the DMA mode.

The device will continue to transfer information until it is

terminated by any one of the following conditions:

s The target changes the SCSI bus phase before the

expected number of bytes are transferred. The

device clears the Command Register (CMDREG)

03H, and generates a service interrupt when the

target asserts

REQ.

s Transfer is successfully complete. If the phase is

Message Out, the device deasserts

ATN before

asserting

ACK for the last byte of the message.

When the target asserts

REQ, a service interrupt is

generated.

s In the Message In phase when the device receives

the last byte. The device keeps the

ACK signal

asserted and generates a Successful Operation

interrupt.

During synchronous data transfers the target may send

up to the maximum synchronous threshold number of

REQ pulses to the initiator. If it is the Synchronous Data-

In phase then the target sends the data and the

REQ

pulses. These bytes are stored by the initiator in the

FIFO as they are received.

Information Transfer Command when issued during the

following SCSI phases and terminating in synchronous

data phases, is handled as described below:

s Message In/Status Phase – When a phase change

to Synchronous Data-In or Synchronous Data-Out is

detected by the device, the Command Register

(CMDREG) 03H is cleared and the DMA interface is

disabled to disallow any transfer of data phase bytes.

If the phase change is to Synchronous Data-In and

bad parity is detected on the data bytes coming in, it

not

reported

since

the

Status

(STATREG) 04H will report the status of the

command just completed. The parity error flag and

the

ATN signal will be asserted when the Transfer

Information command begins execution.

s Message Out/Command Phase – When a phase

change to Synchronous Data-In or Synchronous

Data-Out is detected by the device, the Command

interface is disabled to allow any transfer of data

phase bytes. If the phase change is to Synchronous

Data-In and bad parity is detected on the data bytes

coming in, it is not reported since the Status Register

(STATREG) 04H will report the status of the

command just completed. The parity error flag and

the ATN signal will be asserted when the Transfer

Information command begins execution. The FIFO

Register29 (FFREG) 02H will be latched and will

remain in that condition until the next command

begins execution. The value in the FFREG indicates

the number of bytes in the FIFO when the phase

changed to Synchronous Data-In. These bytes are

cleared from the FIFO, which now contains only the

incoming data bytes.

s In the Synchronous Data-Out phase, the threshold

counter is incremented as

REQ pulses are received.

The transfer is completed when the FIFO is empty

and the Current Transfer Count Register (CTCREG)

00H–01H is zero. The threshold counter will not be

zero.

s In the Synchronous Data-In phase, the Current

Transfer Count Register

(CTCREG) is decre-

mented as bytes are read from the FIFO rather than

being decremented when the bytes are being written

to the FIFO. The transfer is completed when Current

Transfer Count Register (CTCREG) is zero but the

FIFO may not be empty.

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.

AM53C96 Datasheet(PDF) 34 Page - Advanced Micro Devices

AM53C96 Datasheet(HTML) 34 Page - Advanced Micro Devices

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