AM53C94 datasheet(38/63 Pages) AMD

38 / 63 page

P R E L I M I N A R Y

AMD

Am53C94/Am53C96

deasserted at the end of the command which allows the

initiator to send other messages after the ID message is

sent out. Before issuing this command the SCSI

Timeout Register (STIMREG) 05H, the Control Register

One (CNTLREG1) 08H and the SCSI Destination ID

ues. This command will be terminated early if the SCSI

Timeout Register 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 reselection. Upon

disconnecting from the bus the Selection/Reselection

circuit is automatically disabled by device. This circuit

has to be enabled for the device to respond to subse-

quent reselection attempts and the Enable Selection/

Reselection Command is issued to do that. This com-

mand is normally issued within 250 ms (select/reselect

timeout) after the device disconnects from the bus. If

DMA is enabled the device loads the received data to

the buffer memory, but if the DMA is disabled, the re-

ceived 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 Selec-

tion/Reselection Command. The device also generates

a function complete interrupt to the processor. If how-

ever, this command is issued after a bus initiated selec-

tion/reselection has already begun the command is ig-

nored since the Command Register 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 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 three

message bytes. Before issuing this command the SCSI

Timeout Register (STIMREG) 05H, the Control Register

One (CNTLREG1) 08H and the SCSI Destination ID

values. If DMA is enabled, the Start Transfer Count

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 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 Selection Phase

s The target exits the Command Phase early.

General Commands

No Operation Command

(Command Code 00H/80H)

The No Operation Command is used to perform no op-

eration and no interrupt is generated at the end of this

command. This command is issued after the Reset De-

vice Command to enable the Command Register. A No

Operation Command in the DMA mode may be used to

verify the contents of the Start Transfer Count Register

(STCREG) 00H – 01H. After the STCREG is loaded with

the transfer count and a No Operation Command is is-

sued, reading the Current Transfer Count Register

(CTCREG) 00H–01H will give the transfer count value.

Clear FIFO Command

(Command Code 01H/81H)

The Clear FIFO Command is used to initialize the FIFO

to the empty condition. The Current FIFO Register

(CFISREG) 07H reflects the empty FIFO status and the

bottom of the FIFO is set to zero. No interrupt is gener-

ated at the end of this command.

Reset Device Command

(Command Code 02H/82H)

The Reset Device Command immediately stops any de-

vice operation and resets all the functions of the device.

It returns the device to the disconnected state and it also

generates a hard reset. The Reset Device Command re-

mains on the top of the Command Register FIFO hold-

ing the device in the reset state until the No Operation

Command is loaded. The No Operation command

serves to enable the Command Register.

Reset SCSI Bus Command

(Command Code 03H/83H)

The Reset SCSI Bus Command is used to assert the

RSTC signal for approximately 25 ms. This command

causes the device to go to the disconnected state. No

interrupt is generated upon command completion. A

SCSI reset interrupt is however generated upon com-

mand completion if the interrupt is not disabled in the

Control Register One (CNTLREG1) 08H.

AM53C94 Datasheet(PDF) 38 Page - Advanced Micro Devices

AM53C94 Datasheet(HTML) 38 Page - Advanced Micro Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63

Datasheet Download

Link URL