Z
ILOG
Z53C80 SCSI
PRODUCT SPECIFICATION
Z53C80
SMALL COMPUTER
SYSTEM INTERFACE (SCSI)
FEATURES
■ Pin Compatible with the Industry Standard 5380
■ Asynchronous Interface (Supports 3 MB/s)
■ 44-Pin PLCC or 48-Pin DIP Package Styles
■ DMA or Programmed I/O Data Transfers
■ Arbitration Support
■ DirectSCSIBusInterfacewithOn-Board48mADrivers
■ Supports Target and Initiator Roles
■ Meets SCSI Protocol as Defined in ANSI X3.131-1986
Standard
■ Supports Normal or Block Mode DMA
■ Memory or I/O Mapped CPU Interface
■ Added “Glitch Eater” Enhancement to Minimize Bus
Reflection
GENERAL DESCRIPTION
The Z53C80 SCSI (Small Computer System Interface)
controller is designed to implement the SCSI protocol as
defined by the ANSI X3.131-1986 standard, and it is fully
compatible with the industry standard 5380. The device is
capable of operating both as a Target and as an Initiator.
Specialhigh-currentopen-drainoutputsenableittodirectly
interface to the SCSI bus. The Z53C80 has the necessary
interface hook-ups which allow the system CPU to
communicate with it as with any other peripheral device.
The CPU can read from, or write to, the SCSI registers
which are addressed as standard or memory-mapped
I/Os.
The added enhancement known as the “Glitch Eater” is
used to minimize effects of bus reflection on improperly
terminated SCSI bus applications. The high frequency
reflections that can occur on the SCSI bus are filtered out,
reducingthesensitivityoftheinputs,specifically/REQand
/ACKtobussignalreflections.Figure1showsaworstcase
input waveform (labeled A), along with the filtered input
(labeled B) and the output of a Schmitt trigger used to
provide the hysteresis required on SCSI inputs (labeled
C). This enhancement is a requirement for the device to
function properly in a Apple Macintosh® environment.
Notes:
All Signals with a preceding front slash, "/", are active Low, e.g.,
B//W (WORD is active Low); /B/W (BYTE is active Low, only).
The Z53C80 increases the system performance by
minimizing the CPU intervention in DMA operations which
the SCSI controls. The CPU is interrupted by the SCSI
when it detects a bus condition that requires attention. It
also supports arbitration and reselection. The Z53C80 has
theproperhandshakesignalstosupportnormalandblock
modeDMAoperationswithmostDMAcontrollersavailable.
Power connections follow conventional descriptions below:
Connection
Circuit
Device
Power
Ground
VCC
GND
VDD
VSS
® Apple Macintosh is a registered trademark of Apple Computer, Inc.
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PS97SCC0200