Viper 60s Theory Of Operation And Maintenance Manual page 32

4.1 Overview
CHAPTER 4
INTERFACE
INTERFACE
Viper streaming tape drives are designed to operate with the Small Computer System
Interface (SCSI) bus. This chapter discusses SCSI bus operation as it pertains to Viper
drive functions.
SCSI is a standard interface established to support peripheral eqUipment such as printers,
tape drives, magnetic disks, optical disks for microcomputers and other computer sys-
tems. The SCSI bus can support up to eight IDs consisting of any multiple of host adaptors
and peripheral devices.
The interface is an eight-port, daisy-chained bus using eighteen signal lines: nine data-bit
signal lines and nine control lines. The nine data bit lines consist of eight signal lines and
one parity-bit line. The remaining nine lines are for control and status signals to coordi-
nate data transfer operations between the host controller and the selected drive.
The Viper drive has an internal SCSI controller integrated into the drive electronics. Each
device ID on the SCSI bus may drive up to 8 logical units (LUN). The Viper drive
addresses only LUN O.
4.1.1 ANSI SCSI Bus Standards
Besides studying the information presented in this manual, we recommend you read
ANSI X3.131 SCSI bus standard and QIC-l04 (SCSI sequential storage device implemen-
tation standard) before writing host software drivers. See Archive's conformance state-
ment in SPECIFICATIONS.
4.1.2 Signal Notation Conventions
All SCSI bus interface signals are active-low. The following conventions are used to
describe SCSI interface signal notation.
• A signal name or abbreviation preceded by a minus sign (-) indicates the signal is
active low.
Example: -MSG
4-1