Technical data

Table B–1: SCSI Bus Signals
Signal Name Description
Acknowledge (ACK) Set by an initiator to acknowledge a REQ/ACK data transfer handshake.
Attention (AN) Set by an initiator to indicate the Attention condition.
Busy (BSY) Indicates that the bus is being used.
Control/Data (C/D) Indicates whether control information or data is on the bus. A true signal
indicates control.
Data Bits (DB0-7, P) There are eight data bits and a parity bit. DB7 is the most significant bit
and has the highest priority during arbitration. Parity is odd.
Input/Output (I/O) This signal controls the direction of data movement on the bus with
respect to an initiator. A true signal indicates input to the initiator. This
signal is also used to distinguish between the Selection and Reselection
phases.
Message (MSG) This signal is set active by a target during the Message phase.
Request (REQ) This signal is set active by a target to request a REQ/ACK data
handshake.
Reset (RST) Indicates the Reset condition.
Select (SEL) Set active by an initiator to select a target, or by a target to reselect an
initiator.
B–2 Small Computer System Interface (SCSI)