Specifications

ATAPI For Streaming Tape QIC-157 Rev B
3
Write DMA (wo/retry) N CB V V
Write long (w/retry) N* 32 V V
Write long (wo/retry) N* 33 V V
Write multiple N C5 V V
Write same N E9 V V
Write sector(s) (w/retry) N* 30 V V
Write sector(s) (wo/retry) N* 31 V V
Write verify N 3C V V
Invalid command code V V V V
V = valid on this command
M = Mandatory and shall be supported by ATAPI Devices, as specified by the ATA Standard
O = Optional for use by an ATAPI Device
N = Not supported by ATAPI Devices (shall be Aborted by the ATAPI Device)
* The ATA Standard specifies command as Mandatory
1.5. How SCSI is Used by ATAPI
Although the ATAPI Device will utilize many of the actual packet definitions from the SCSI
standard, it will NOT use most other features of the normal SCSI Protocol. Thus there are no
Phases, no Messages, no sharable bus, (only one Host Computer) and no SCSI Hardware. For those
who are familiar with the current SCSI-3 effort, this specification will not conform with that
Packetized Standard, due mostly to limitations of ATAPI.
1.6. Differences from the SCSI Standard
Some of the major differences from the SCSI Standard:
• Status shall use the ATAPI description, rather than a Data Byte passed at the end of the
command.
• ATAPI Device is slave during operation rather than the master view of a SCSI Peripheral.
• No messages are supported.
• No disconnect/reconnect or any of the SCSI Pointers.
• No linking or queuing of commands.
• All Streaming Tape Command Packets (CP) are 12 bytes in length, rather than the 6, 8, 10 or
12-byte packets of the SCSI Standard; however, 16-byte ATAPI Command Packets are defined
for future Devices. The size of the Command Packet required by a Device is defined in word 0
of the ATAPI Identify Device command, allowing Host Device Drivers to determine the size of
the Command Packets before issuing an ATAPI Command Packet.
• No allegiance conditions are used.
This specification will make use of many of the Standard SCSI Command Descriptor Block
definitions and Commands, but some of the commands that would normally be supported by a SCSI
Device will not be supported for various reasons. These commands are:
• RESERVE and RELEASE; as there is only one Host allowed, this is not needed.
• CHANGE DEFINITIONS; as there is no SCSI, this command is nonsensical.
• COPY, COPY/VERIFY; no shared bus so this command cannot be implemented.