Z
ILOG
Z5380 SCSI
FUNCTIONAL DESCRIPTION (Continued)
This bit should also be set during DMA send operations.
Bit 1. Assert /ATN. /ATN may be asserted on the SCSI Bus
by setting this bit to a one (1) if the Target Mode bit (Mode
Register, bit 6) is False. /ATN is normally asserted by the
initiator to request a Message Out bus phase. Note that
sinceAssert/SELandAssert/ATNareinthesameregister,
a select with /ATN may be implemented with one CPU
write. /ATN may be deasserted by resetting this bit to zero.
A read of this register simply reflects the status of this bit.
Address: 1
(Read Only)
D7 D6 D5 D4 D3 D2 D1 D0
Assert Data Bus
Assert /ATN
Assert /SEL
Assert /BSY
Bit 2. Assert /SEL. Writing a one (1) into this bit position
asserts /SEL onto the SCSI Bus. /SEL is normally asserted
after Arbitration has been successfully completed. /SEL
may be disabled by resetting bit 2 to a zero. A read of this
register reflects the status of this bit.
Assert /ACK
Lost Arbitration
Arbitration in Progress
Assert /RST
Bit 3. Assert /BSY. Writing a one (1) into this bit position
asserts /BSY onto the SCSI Bus. Conversely, a zero resets
the /BSY signal. Asserting /BSY indicates a successful
selection or reselection. Resetting this bit creates a Bus-
Disconnect condition. Reading this register reflects bit
status.
Figure 6. Initiator Command Register
Address: 1
(Write Only)
D7 D6 D5 D4 D3 D2 D1 D0
Bit4.Assert/ACK. Bit4isusedbythebusinitiatortoassert
/ACK on the SCSI Bus. In order to assert /ACK, the Target
Mode bit (Mode Register, bit 6) must be False. Writing a
zero to this bit deasserts /ACK. Reading this register
reflects bit status.
Assert Data Bus
Assert /ATN
Assert /SEL
Assert /BSY
Assert /ACK
"0"
Bit 5. “0” (Write Bit). Bit 5 should be written with a zero for
proper operation.
Test Mode
Assert /RST
Bit 5. LA (Lost Arbitration - Read Bit). Bit 5, when active,
indicates that the SCSI detected a Bus-Free condition,
arbitrated for use of the bus by asserting /BSY and its ID on
the Data Bus, and lost Arbitration due to /SEL being
asserted by another bus device. This bit is active only
when the Arbitrate bit (Mode Register, bit 0) is active.
Figure 7. Initiator Command Register
The following describes the operation of all bits in the
Initiator Command Register:
Bit 6. Test Mode (Write Bit). Bit 6 is written during a test
environment to disable all output drivers, effectively re-
movingtheZ5380fromthecircuit.Resettingthisbitreturns
the part to normal operation.
Bit 0. Assert Data Bus. This bit, when set, allows the
contentsoftheOutputDataRegistertobeenabledaschip
outputs on the signals /DB7-DB0. Parity is also generated
and asserted on /DBP.
Bit 6. AIP (Arbitration in Process - Read Bit). Bit 6 is used
to determine if Arbitration is in progress. For this bit to be
active, the Arbitrate bit (Mode Register, bit 0) must have
been set previously. It indicates that a Bus-Free condition
has been detected and that the chip has asserted /BSY
and put the contents of the Output Data Register onto the
SCSI Bus. AIP will remain active until the Arbitrate bit is
reset.
When connected as an Initiator, the outputs are only
enabled if the Target Mode bit (Mode Register, bit 6) is 0,
the received signal I//O is False, and the phase signals (C/
/D, I//O, and /MSG) match the contents of the Assert C//D,
Assert I//O, and Assert /MSG in the Target Command
Register.
Bit 7. Assert /RST. Whenever a one is written to bit 7 of the
Initiator Command Register, the /RST signal is asserted on
6
PS97SCC0100
PS009101-0201