
Register Descriptions
4-7
ADB
Assert SCSI Data Bus
When this bit is set, the SYM53C710 drives the contents
of the
SCSI Output Data Latch (SODL)
register onto the
SCSI data bus. When the SYM53C710 is an initiator, the
SCSI I/O signal must be inactive to assert the SODL
contents onto the SCSI bus. When the SYM53C710 is a
target, the SCSI I/O signal must be active to assert the
SODL contents onto the SCSI bus. The contents of the
SODL register can be asserted at any time, even before
the SYM53C710 is connected to the SCSI bus. Clear this
bit when executing SCSI SCRIPTS. It is normally used
only for diagnostic testing or operation in low level mode.
6
ESR
Enable Selection and Reselection
When this bit is set, the SYM53C710 responds to bus
initiated selections and reselections. The SYM53C710
can respond to selections and reselections in both
initiator and target roles. If SCSI Disconnect/Reconnect is
to be supported, set this bit as part of the initialization
routine. This bit is cleared after Disconnect/Reselection.
5
CON
Connected
This bit is automatically set any time the SYM53C710 is
connected to the SCSI bus as an initiator or as a target.
It is set after the SYM53C710 successfully completes
arbitration or when it responds to a bus initiated selection
or reselection. This bit is also set after the chip wins
simple arbitration when operating in low level mode.
When this bit is cleared, the SYM53C710 is not
connected to the SCSI bus. This bit is automatically
cleared when Bus Free phase is detected.
4
The CPU can force a connected or disconnected
condition by setting or clearing this bit. This feature is
used primarily during loopback mode.
RST
Assert SCSI RST/ Signal
Setting this bit asserts the RST/ signal. The RST/ signal
remains asserted until this bit is cleared. The 25
μ
s
minimum assertion time defined in the SCSI specification
must be timed out by the controlling microprocessor or a
SCRIPTS delay routine. The RST/ signal asserts within
40 clocks and generates an interrupt if enabled in
SCSI
Interrupt Enable (SIEN)
.
3