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ST43401N/ND and ST43402ND Reference Manual, Rev. C
Table 6. SCSI bus signal lines
Signal
Data Bus (DB 15–0+P)
Busy (BSY)
Select (SEL)
Reset (RST)
Attention (ATN)
Acknowledge (ACK)
Request (REQ)
Message (MSG)
Input/Output (I/O)
Control/Data (C/D)
T = target and I = initiator
Source
Function
I–T
Sixteen data-bit signals, plus a parity bit signal
that form the Data Bus. DB(15) is the most-
significant bit and has the highest priority dur-
ing the Arbitration phase. Bit number, signifi-
cance, and priority decrease downward to
DB(0). A data bit is defined as 1 when the signal
is true and 0 when false. Data parity DB(P) is
odd. The use of parity is a selectable option and
is not valid during the Arbitration phase.
I–T
An "or-tied" signal that indicates to the initiator
or target that the bus is being used.
I–T
Used by an initiator to select a target, or by a
target to reselect an initiator.
I–T
An "or-tied" signal that indicates the Reset
condition exists.
I
Driven by the initiator to indicate an Attention
condition.
I
Driven by the initiator to acknowledge a REQ/
ACK data transfer handshake.
T
Driven by the target to indicate a request for a
REQ/ACK data transfer handshake.
T
Driven by target during the Message phase.
T
Driven by the target to control the direction of
data movement on the data bus with respect to
the initiator. True indicates input to the initiator.
Also used to distinguish between Selection
and Reselection phases.
T
Driven by the target to indicate whether control
or data information is on the data bus. True
indicates control.
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