AM53CF94 Advanced Micro Devices, AM53CF94 Datasheet - Page 42

• Manufacturer Part Number: AM53CF94
• Description: Enhanced SCSI-2 Controller (ESC)
• Manufacturer: Advanced Micro Devices

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
is enabled, the Start Transfer Count Register
(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
Register times out or if the Target does not go to the
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
Register (STIMREG), the Control Register One
(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:
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-
42
The SCSI Timeout Register times out
The Target does not go to the Message Out Phase
following the Selection Phase
The Target exits the Message Phase early
The Target does not go to the Command Phase
following the Message Out Phase
The Target exits the Command Phase early
AMD
Am53CF94/Am53CF96
P R E L I M I N A R Y
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
Register (SDIDREG) must be set to the proper values
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