Scsi Id Bits; Scsi Signals; Scsi Signal Definitions; Table 3-3 Scsi-2 Bus Signal Definitions - Quantum DLT 4000 Product Manual

SCSI Description

3.3.2 SCSI ID Bits

SCSI permits a maximum of eight SCSI devices on a SCSI bus (16 devices are
permitted when using wide SCSI). Each SCSI device has a unique SCSI ID
assigned to it. This SCSI ID provides an address for identifying the device on the
bus. On the drive, the SCSI ID is assigned by configuring jumpers or connecting
remote switches to the option connector. Chapter 2, Hardware Implementation
has full instructions for setting the SCSI ID.
3.4

SCSI SIGNALS

The following paragraphs define SCSI signals and bus timing values.

3.4.1 SCSI Signal Definitions

Table 3–3 defines the SCSI bus signals.
Signal Definition
ACK A signal driven by the initiator as an acknowledgment of receipt of
(acknowledge) data from a target or as a signal to a target indicating when the target
should read the data (out) lines.
ATN (attention) A signal driven by an initiator to indicate that it has a message to send.
BSY (busy) An OR-tied signal that indicates that the bus is in use.
C/D A signal driven by a target that indicates whether CONTROL or DATA
(control/data) information is on the DATA BUS. True (low voltage) indicates
CONTROL.
DB(7–0,P) Eight data-bit signals, plus a parity-bit signal that form a DATA BUS.
(data bus) DB(7) is the most significant bit and has the highest priority (8 or 16-
bit) during ARBITRATION. Bit number, significance, and priority
decrease downward to DB(0). A data bit is defined as 1 when the
signal value is true (low voltage) and 0 when the signal value is false
(high voltage). Data parity DB(P) is odd. Parity is undefined during
ARBITRATION.
3-6
Table 3–3 SCSI-2 Bus Signal Definitions
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