Adaptec AHA-1740A Product manual

adaptec
AHA-1740A/1742A/1744
EISA-to-Fast SCSI Host Adapter
Technical Reference Manual

Copyright
© Copyright 1992 Adaptec, Inc. All rights reserved. No part of this publication may be reproduced, stored in a re-
trieval system, or transmitted in any form or by any means; electronic, mechanical, photocopying, recording or
otherwise, without the prior written consent of Adaptec, Inc., 691 South Milpitas Blvd., Milpitas, CA 95035.
Trademarks
EISA is a registered trademark of BCPR Services Inc.
Intel is a registered trademark, and 286, 386 are trademarks of
Intel Corporation.
IBM, OS/2, PC AT, and Micro Channel are registered trademarks of International
Business MachinesCorporation.
MS-DOS, MS,Windows, Xenix, and Microsoft are registered trademarks of
Microsoft Corporation.
Novell and NetWare are registered trademarks of Novell, Inc.
QEMMis a trademark of Quarterdeck Office Systems.
SCO is a trademark of the Santa Cruz Operation.
SYTOS and Sytos Plus are trademarks of Sytron Corporation.
QRAM, Move ’Em, and 386-Max are trademarks of Qualitas, Inc.
UNIX is a registered trademark of AT&T Bell Laboratories.
Changes
The material in this manual is for information only and is subject to change without notice. While reasonable ef-
forts have beenmade in the preparation of this manual to assure its accuracy, Adaptec, Inc. assumes no liability
resulting from errors or omissions in thismanual, or fromtheuse of the informationcontained herein.
Adaptec reserves the right to make changes in the product designwithout reservation andwithout notification to
its users.
Additional information may be obtained from:
adaptec
Literature Department - MS/40
691 South Milpitas Blvd.
Milpitas, CA 95035
ii

FCC Compliance Statement
NOTE: This equipment has been tested and foundto complywith the limits for aClassB digital device, pursuant
to Part 15 of the FCC rules. These limits are designed to provide reasonable protection against harmful interfer-
ence in residential installations. This equipment generates, uses, and can radiate radio frequency energy, and if
not installed and used in accordance with the instructions, may cause harmful interference to radio communica-
tions. However, there is no guarantee that interference will not occur ina particular installation.
If this equipment does cause interference to radio or television equipment reception, which can be determined by
turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the
followingmeasures:
•Reorient or relocate the receiving antenna
•Move the equipment away from the receiver
•Plug the equipment into an outlet on a circuit different from that to which the receiver is powered
•If necessary, the user should consult the dealer or an experienced radio/television technician for ad-
ditional suggestions
CAUTION: Only equipment certified to comply withClass B(computer input/output devices, terminals, printers,
etc.) should be attached to this equipment, and must have shielded interface cables.
Finally, any change or modifications to the equipment by the user not expressly approved by the grantee or
manufacturer could void the user’s authority to operate such equipment.
Each AHA-1740A/1742A/1744 is equipped with an FCC compliance label which shows only the FCC Identifica-
tion number. This device complies with part15 of the FCC rules. Operation is subject to the following two condi-
tions: (1) this device may not cause harmful interference and (2) this device must accept anyinterference
received, including interference thatmay cause undesired operation.
iii

iv

Table of Contents
Preface...............................................................................................................................xi
Conventions......................................................................................................................xii
Chapter One - Introduction
Document Scope..............................................................................................................1-1
Purpose............................................................................................................................1-1
AHA-1740A/1742A/1744 Product Features...................................................................1-2
EISA Features..........................................................................................................1-2
SCSI Features ..........................................................................................................1-2
Board Features.........................................................................................................1-3
Configuration Diskette and Installation Guide (ASW-C174).......................................1-4
Product Specifications....................................................................................................1-5
Extended Industry-Standard Architecture Interface...................................................1-5
Standard EISA Bus Electronic and Physical Interface .........................................1-5
SCSI Interface.................................................................................................................1-6
Electrical Interface for AHA-1740A/1742A ............................................................1-6
Electrical Interface for AHA-1744...........................................................................1-7
Internal Connector...................................................................................................1-7
External Connector..................................................................................................1-8
Floppy Disk Interface.....................................................................................................1-9
Standard Electronic and Physical interface ...........................................................1-9
Connector..................................................................................................................1-9
Radiation Immunity .......................................................................................................1-9
Reference Documents .....................................................................................................1-9
Chapter Two - Architecture
Hardware ........................................................................................................................2-1
Bus Master DMA......................................................................................................2-2
SCSI Interface and Protocol Chip (AIC-6251)........................................................2-2
8- and 16-Bit Memory and Odd Byte Data Transfers............................................2-3
Bus Auxiliary Interface Chip (AIC-565) .................................................................2-3
EISA Configuration Chip (AIC-575) .......................................................................2-4
BMIC Bus Interface Chip (82355)...........................................................................2-4
Floppy Disk Controller (AHA-1742A Only)............................................................2-4
Standard Mode Firmware..............................................................................................2-5
Mailboxes..................................................................................................................2-5
Command Control Block..........................................................................................2-6
Command Descriptor Block ....................................................................................2-7
Principles of Operation............................................................................................2-8
Task Queuing ...........................................................................................................2-8
Enhanced Mode Firmware.............................................................................................2-9
Onboard BIOS Operation.............................................................................................2-11
Power-Up Diagnostics ..................................................................................................2-11
v

ASW-C174 Configuration Diskette..............................................................................2-12
Chapter Three - Installation
Unpacking and Inspection..............................................................................................3-1
Installation......................................................................................................................3-1
System Configuration Background for Standard Mode.........................................3-2
Preparation...............................................................................................................3-2
Termination..............................................................................................................3-3
SCSI Addressing (ID)...............................................................................................3-3
SCSI Parity...............................................................................................................3-4
Hardware Installation .............................................................................................3-4
Checklist...................................................................................................................3-7
Terminators..............................................................................................................3-7
System Configuration.....................................................................................................3-7
MCS Configuration ..................................................................................................3-9
Standard Mode SCSI Configuration.....................................................................3-11
Enhanced Mode SCSI Configuration ....................................................................3-12
Multiple Adapters Sharing Same SCSI Bus.........................................................3-14
Phoenix Configuration...........................................................................................3-15
Floppy Disk Configuration.....................................................................................3-15
ADL Utility....................................................................................................................3-15
ADL Operation..............................................................................................................3-16
List of Adapters......................................................................................................3-16
Main Menu..............................................................................................................3-16
Download Firmware (AHA-1740/1744 Only)........................................................3-17
Firmware Information (AHA-1740/1744/1740A/1742A) ......................................3-18
Low-level Format ...................................................................................................3-18
Chapter Four - Hardware Functional Description
Hardware Overview........................................................................................................4-1
Standard Mode I/O Port Interface.................................................................................4-1
I/O Port Interface Bit Definition .............................................................................4-2
Control and Status Port...........................................................................................4-3
Command/Data Out and Data In Port....................................................................4-5
Interrupt Flag Port ..................................................................................................4-6
Reset Functions ..............................................................................................................4-8
Hard Reset Operations ............................................................................................4-8
SCSI Reset Operations ............................................................................................4-9
SCSI Soft Reset Option............................................................................................4-9
SCSI Hard Reset Option .......................................................................................4-10
EISA Expansion Identifiers .........................................................................................4-10
Expansion Board ID Registers ..............................................................................4-11
Board Configuration Registers..............................................................................4-12
I/O Port Register Standard Mode (Group 1).........................................................4-17
I/O Port Register Enhanced Mode (Group 2)........................................................4-20
Diskette Registers.........................................................................................................4-23
Table of Contents
vi

Digital Output Registers (Write 3F2) ...................................................................4-23
Diskette Controller Registers (Read/write 3F4 and 3F5) ....................................4-24
Digital Input Register (Read 3F7).........................................................................4-25
Diskette Control Register (Write 3F7)..................................................................4-25
Firmware Download (AHA-1740/1744 Only) ..............................................................4-26
Hardware Configuration Requirements......................................................................4-27
SCSI Configuration................................................................................................4-27
BIOS Driver Needs ................................................................................................4-28
SCSI Subsystem Configuration.............................................................................4-28
Initialize SCSI Subsystem Command (Standard Mode)......................................4-28
Initialize SCSI Subsystem Command (Enhanced Mode).....................................4-28
Configuration Byte Description and Defaults......................................................4-29
Chapter Five - Standard Mode Firmware Description
Host Adapter Command Overview................................................................................5-1
No Operation (Operation Code 00)..........................................................................5-2
Mailbox Initialization (Operation Code 01)............................................................5-2
Start SCSI Command (Operation Code 02)............................................................5-3
Start PC AT BIOS Command (Operation Code 03) ...............................................5-3
Adapter Inquiry (Operation Code 04) .....................................................................5-3
Enable Mailbox Out Available Interrupt (Operation Code 05) .............................5-4
Set Selection Time out (Operation Code 06)...........................................................5-5
Set Bus On Time (Operation Code 07)....................................................................5-5
Set Bus Off Time (Operation Code 08)....................................................................5-6
Set Transfer Speed (Operation Code 09) ................................................................5-6
Return Installed Devices (Operation Code 0A) ......................................................5-7
Return Configuration Data (Operation Code 0B)...................................................5-8
Enable Target Mode Command (Operation Code 0C)............................................5-9
Return Setup Data (Operation Code 0D)..............................................................5-10
Initialize SCSI Subsystem (Operation Code 10) ..................................................5-12
Return Firmware Checksum (Operation Code 11)...............................................5-12
Write Adapter Channel 2 Buffer (Operation Code 1A)........................................5-12
Read Adapter Channel 2 Buffer (Operation Code 1B).........................................5-13
Write Adapter FIFO Buffer (Operation Code 1C)................................................5-13
Read Adapter FIFO Buffer (Operation Code 1D).................................................5-13
Echo Command Data (Operation Code 1F) ..........................................................5-14
Adapter Diagnostic (Operation Code 20)..............................................................5-14
Set Host Adapter Options (Operation Code 21) ...................................................5-14
Mailbox Overview.........................................................................................................5-14
Mailbox Out Definition ..........................................................................................5-15
Mailbox In Definition.............................................................................................5-17
Command Block Definition..........................................................................................5-20
Command Control Block Format ..........................................................................5-20
Scatter/Gather List Definition.....................................................................................5-28
Description of Operation ..............................................................................................5-29
Execution of Initiator Mode Operations ..............................................................5-29
Execution of Target Mode Operations With a Prepared CCB.............................5-30
Execution of Target Mode Operations Without a Prepared CCB........................5-31
DMA Channel Initialization (with Host Adapter BIOS Disabled) ............................5-31
Table of Contents
vii

Interrupt Initialization.................................................................................................5-32
Chapter Six - Enhanced Mode Firmware Description
Introduction.....................................................................................................................6-1
Control Block...................................................................................................................6-3
Command Word........................................................................................................6-4
Flag Word 1 ..............................................................................................................6-4
Flag Word 2 ..............................................................................................................6-6
Data or Scatter/Gather List Pointer .....................................................................6-10
Data or Scatter/Gather List Length......................................................................6-11
Status Block Pointer ..............................................................................................6-11
Chain Address ........................................................................................................6-12
Sense Information Pointer.....................................................................................6-12
Sense Length..........................................................................................................6-12
CDB Length............................................................................................................6-12
Checksum of Data..................................................................................................6-12
SCSI Command Descriptor Block .........................................................................6-13
Status Block..................................................................................................................6-13
Status Word............................................................................................................6-14
Host Adapter Status...............................................................................................6-17
Target Status..........................................................................................................6-17
Residual Byte Count ..............................................................................................6-18
Residual Buffer Address........................................................................................6-18
Additional Status Length ......................................................................................6-19
Sense Length..........................................................................................................6-19
Target Mode CDB...................................................................................................6-19
Control Block Commands.............................................................................................6-19
Download Firmware...............................................................................................6-21
Initialize SCSI Subsystem.....................................................................................6-23
Initiator SCSI Command.......................................................................................6-26
No Operation ..........................................................................................................6-27
Read Host Adapter Inquiry Data ..........................................................................6-29
Read Sense Information.........................................................................................6-34
Run Diagnostic Test...............................................................................................6-36
Target SCSI Command..........................................................................................6-38
Aborting Control Block Commands.............................................................................6-39
Control Block is Queued for Operation.................................................................6-40
Associated Target for the Control Block is Disconnected ....................................6-40
Control Block is Currently Active on the SCSI Bus.............................................6-40
Control Block in the Interrupt Queue...................................................................6-40
Asynchronous Event Notification ................................................................................6-41
Asynchronous Event Conditions ...........................................................................6-41
SCSI Bus Reset ......................................................................................................6-41
Host Adapter Selected by Another Initiator.........................................................6-42
Immediate Commands..................................................................................................6-42
Reset........................................................................................................................6-43
Reset Device ...........................................................................................................6-43
Reset Host Adapter................................................................................................6-45
Resume....................................................................................................................6-46
Table of Contents
viii

SCSI Bus Reset Handling............................................................................................6-46
Reset Initiated by the Host....................................................................................6-46
Reset Initiated by the Host Adapter .....................................................................6-47
Reset Initiated by Another SCSI Device...............................................................6-47
Chapter Seven - Onboard BIOS Interface
Introduction ....................................................................................................................7-1
Operation with the Standard Interface.........................................................................7-1
No Standard Hard Disks Installed..........................................................................7-2
One Standard Hard Disk Installed.........................................................................7-2
Two Standard Internal Hard Disks Installed ........................................................7-2
Enhanced Interface Operation.......................................................................................7-2
Hardware..................................................................................................................7-2
Initialization.............................................................................................................7-2
Boot Issues................................................................................................................7-4
Interrupt 13h Interface Functionality...........................................................................7-5
Physical to Logical Block Address Translation......................................................7-5
Virtual to Physical Buffer Address Translation.....................................................7-5
BIOS Command Return Codes................................................................................7-6
Hardware BIOS Commands....................................................................................7-7
Int 15h Functionality......................................................................................................7-9
Differences Between Operating Modes .........................................................................7-9
Multiple Adapter Support............................................................................................7-10
Chapter Eight - Device Drivers
DOS Operation without Drivers....................................................................................8-1
Standard Mode.........................................................................................................8-1
Enhanced Mode........................................................................................................8-1
System Configuration.....................................................................................................8-1
Low-Level Format...........................................................................................................8-2
Installation and Initialization Under DOS...................................................................8-2
Managers.........................................................................................................................8-3
DOS Manager...........................................................................................................8-4
Microsoft Windows 3.0 and Extended Memory Managers ....................................8-5
OS/2 Manager...........................................................................................................8-5
Novell NetWare Manager........................................................................................8-6
Unix/Xenix Manager................................................................................................8-6
Chapter Nine - SCSI Features
Initiator Mode SCSI Description ...................................................................................9-1
Linked SCSI Commands..........................................................................................9-2
Zero Latency Read Operation..................................................................................9-2
Table of Contents
ix

SCSI Messages .........................................................................................................9-3
Target Mode SCSI Description ......................................................................................9-3
Initiator Conformance Level Requirements...........................................................9-3
Synchronous Transfer Support ...............................................................................9-4
SCSI Target Operation in Processor Target Mode.................................................9-4
Incorrect Length Management for Target Mode Operation ..................................9-9
Aborting Target Mode Commands ........................................................................9-10
Chapter Ten - Problem Determination
Self Diagnostic Capability............................................................................................10-1
Indicators ......................................................................................................................10-2
Problems Detected During Operation .........................................................................10-2
HA Status Error Indications and Corrective Actions ..........................................10-3
SCSI Error Indications and Corrective Actions ...................................................10-5
Problems Detected During Installation.......................................................................10-6
Chapter Eleven - Glossary
Glossary of Terms.........................................................................................................11-1
Appendix A - Memory Cycle Timing Diagram
AHA-1740A/1742A/1744 Timing Diagram................................................................... A-1
Appendix B - Connector Pinout
Internal Connector Pin Assignments ........................................................................... B-1
External Connector Pin Assignments .......................................................................... B-3
Appendix C - Register Reference
System Register Reference............................................................................................ C-1
Appendix D - EISA Free-Form Data
SCSI Subsystem Data Structure ..................................................................................D-1
Table of Contents
x

Preface
This Technical Reference Manual provides technical information for Adaptec’s
AHA-1740A/1742A/1744 EISA-to-Fast SCSI Host Adapters. It is prepared for cus-
tomer technical personnel requiring detailed information on the operation of the
board at a register and command protocol level. Documentation of board schematics,
integrated circuits, microcode and BIOS routines is not provided.
Programmers writing device drivers for specific perpherals are strongly advised to
use the Advanced SCSI Programming Interface (ASPI) specification appropriate to
the operating system chosen. This will allow flexibility across all boards complying
with ASPI Manager modules and prevent obsolescence. Please contact Adaptec
Corporate Communications for copies of ASPI specifications. Software managers are
documented and sold separately.
Every effort has been made to ensure the technical accuracy of this reference man-
ual. If you believe that inaccuracies exist, please communicate this information in
writing to your local field applications support personnel or directly to the product
manager.
xi

Conventions
The following typographic conventions are used throughout this Technical Reference
Manual.
bold
Used for keystrokes (.. press the Enter key ..) and screen selection fields (.. select
Backup Device and ..).
Helvetica
Used for operator entry that must be typed exactly as shown
( .. device=c:\cdrom\cdrom.tsd ..) and for screen messages (.. Enter Password ..).
Helvetica Italics
Used as a placeholder for text you must determine and type in (.. enter nn for number
..). Also used for program and file names in body text (.. the
autoexec.bat file ..).
Italics
Used for emphasis (.. is only supported ..) and document reference (.. refer to Chapter
Three, Installation ..).
ALL CAPITALS
Used for acronyms (..the SCSI device..).
❏
xii

Chapter One
Introduction
Document Scope
This manual provides information on installation and defines the program interfaces
of the AHA-1740A/1742A/1744 intelligent host adapters in EISA bus-based systems.
Programming peripheral drivers directly to the hardware interface of the board is not
recommended. The ASPI (Advanced SCSI Programming Interface) specifications pro-
vide a simpler and more flexible interface which is protected against changes, up-
grades and obsolescence of the boards.
Purpose
The Adaptec AHA-1740A/1742A/1744 provides a powerful multitasking interface be-
tween the Extended Industry Standard Architecture (EISA) bus and the Small Com-
puter System Interface (SCSI) bus.
The AHA-1740A/1742A/1744 is a high-performance intelligent host adapter which
supports a maximum asynchronous SCSI rate of 2.0 MBytes/second and a synchro-
nous transfer rate of 10.0 MBytes/second. It supports multithreaded I/O operations,
allowing simultaneous operations on multiple targets/LUNs. Disconnect/Reconnect
support maximizes bus utilization for multiple target systems. Target mode opera-
tion allows the AHA-1740A/1742A/1744 to receive information from other host adapt-
ers. Scatter/Gather allows high performance even in systems with fragmented
memory buffers.
The AHA-1740A/1742A/1744 provides a solution for system applications requiring
very high performance, configuration flexibility, multithreaded I/O capability, and
system redundancy. The Adaptec BIOS also allows the AHA-1740A/1742A/1744 to be
used in place of a standard hard disk controller.
The AHA-1740A/1742A host adapter provides high-performance host adapter cir-
cuitry connected to the more common single-ended SCSI bus. The SCSI specification
recommended maximum cable length for 5 MBytes/second synchronous data transfer
is 6 Meters, or about 20 feet.
The AHA-1744 host adapter provides identical host adapter circuitry, but connects to
a differential SCSI bus. The SCSI specification recommended maximum cable length
for 5 MBytes/second synchronous data transfer is 25 Meters, or about 82 feet.
1-1

AHA-1740A/1742A/1744 Product Features
EISA Features
The AHA-1740A/1742A/1744 is a full-performance EISA board offering the highest
performance available across the bus. It takes advantage of first-party DMA opera-
tions, also known as bus mastering, which allow data transfers to proceed at high
data rates without system processor intervention. The main EISA functions which
come standard on the board include:
•Auto Configuration Support
•High-performance Bus Master transfers with burst cycles which provide a
data rate of 33 MBytes/second
•32-bit data path
•32-bit address space
•Even or odd starting address and byte count handling
•1K FIFO for efficient data transfer
•Interrupts enabled/disabled through I/O port write
•Interrupts configurable for either edge or level trigger
•Dual Control Interface, AHA-1540 family-compatible (Standard Mode) or
EISA-SCB compatible (Enhanced Mode)
SCSI Features
Adaptec has long been a supplier of leading edge SCSI products and the AHA-
1740A/1742A/1744 is no exception. The board uses industry-standard protocol ICs
which fully comply with the 1990 ANSI SCSI specification, including:
•Maximum synchronous SCSI transfer rate of 10.0 MBytes/second (Fast SCSI)
•Asynchronous and synchronous peripherals supported simultaneously
•Disable synchronous negotiation independently on each target as a configura-
tion option
•Disable disconnection independently on each target as a configuration option
•Supports Modify Data Pointer message (Zero Latency Reads)
•High-density SCSI-2 connector
•Non-destructive current limit on terminator power supply
adaptec AHA-1740A/1742A/1744
1- 2

•Internal and external SCSI connectors
•Initiator and target modes of operation fully supported
•Differential SCSI (AHA-1744 only)
•SCSI-1 and SCSI-2 compatible
•Tagged queuing
Board Features
In addition to extensive functions on the two main interfaces of the board, the intelli-
gence built into the board microcode and BIOS software allows a number of addi-
tional functions to be offered, including:
•Scatter/Gather operation
•Boot from any target (set as configuration option)
•Compatible with existing AHA-1540 family driver software (ASW-1400 series
managers)
•True multithreaded operation supporting up to 255 tasks simultaneously
•Programmable mailbox architecture
•Bootable BIOS for standard hard disk emulation
•Floppy Diskette Controller (AHA-1742A only)
While all versions of the board fully support all of the above features, they are distin-
guished by:
•AHA-1740A Fast SCSI-to-EISA Host Adapter
•AHA-1742A Fast SCSI-to-EISA Host Adapter with floppy diskette controller
•AHA-1744 Fast differential SCSI-to-EISA Host Adapter
The AHA-1740A/1742A/1744 microcode is available in two separate versions which co-
exist simultaneously in the onboard PROM, but must be configured into one of the
two available modes:
•Standard Mode
•Enhanced Mode
The modes cannot operate simultaneously. The EISA Configuration Utility (ECU)
must be run to select one of the modes (Refer to Chapter Three, Installation). The
EISA-to-Fast SCSI Host Adapter Introduction
1-3

mode dictates the software manager revision which can support the board, but has
no effect on the SCSI or host bus hardware connections.
Standard Mode allows software drivers written for the AHA-1540 or AHA-1640 fami-
lies to run unaltered on the AHA-1740 family. There is no performance penalty for
this on the EISA bus. The AHA-1740A/1742A/1744 still performs 32-bit transfers at
speeds up to 33 MBytes/second.
Enhanced Mode allows the board to take advantage of a number of features which
were not available on earlier host adapters. These include:
•Fast SCSI data transfer
•32-bit addressing capability
•Ability to access all EISA board registers
•Single fast mailbox handling
•Tagged queuing (SCSI)
•Fully configurable SCSI bus options for each SCSI target ID
Configuration Diskette and Installation Guide (ASW-C174)
As with other EISA boards, the AHA-1740A/1742A/1744 is configured by the EISA
Configuration Utility (ECU) that came with your EISA computer. The ASW-C174
diskette contains the configuration and overlay files required by the ECU for the
AHA-1740A/1742A/1744. In addition, the ASW-C174 contains a utility for checking
the version of microcode in your AHA-1740A/1742A/1744 and for low-level formatting
of hard disks.
Note
The AHA-1740/1744 stores microcode in an E2PROM. You can download microcode
to it by using the
adl.exe download utility included on the ASW-C174. The AHA-
1740A/1742A stores microcode in an EPROM. The A version boards do not support
the download feature.
adaptec AHA-1740A/1742A/1744
1- 4

Product Specifications
Physical Dimensions
Length 13-3/8 inches
Width 5/8 inch
Height 5 inches
Standard EISA-compatible form factor.
Power Requirements
+5.0 +/- 0.25 Volts at 2.9 Amps maximum.
Environmental Requirements
Temperature 0-55oC (operating or storage)
Reliability Information
Mean Time Between Failures: 100,000 hours
(calculated per Mil Handbook 217E, ground benign, 40oC)
Mean Time Between Failures: (calculated)
1740A 61,466 hours
1742A 60,589 hours
1744 54,856 hours
Mean Time to Repair: 30 minutes
Extended Industry-Standard Architecture Interface
Standard EISA Bus Electronic and Physical Interface
Driver Output Signals
VOL 0 volts minimum 0.4 volts maximum
IOL 24 mA
VOH 2.4 volts minimum 5.25 volts maximum
IOH 8 mA
Receiver Input Signals
VIL 0.8 volts maximum
VIH 2.0 volts minimum
Connector configuration as specified by manual of Extended Industry Standard Archi-
tecture host computer.
EISA-to-Fast SCSI Host Adapter Introduction
1-5

SCSI Interface
Electrical Interface for AHA-1740A/1742A
As specified by ANSI X3.131-1986 for single-ended operation.
Output Signals
All signals use open collector or three-state drivers. Each signal driven by a SCSI de-
vice has the following output characteristics when measured at the SCSI device’s
connector:
Signal Definition Characteristics
VOL Low-level output voltage 0.0 to 0.5 volts DC at 48 mA sinking (signal
assertion)
VOH High-level output voltage 2.5 to 5.25 volts DC (signal negation)
Input Signals
SCSI inputs meet the following electrical characteristics on each signal (including
both receivers and passive drivers):
Signal Definition Characteristics
VIL Low-level input voltage 0.0 to 0.8 volts DC (signal true)
VIH High-level input voltage 2.0 to 5.25 volts DC (signal false)
IIL Low-level input current -0.4 to 0.0 mA at V1= 0.5 volts DC
IIH High-level input current 0.0 to 0.1 mA at V1= 2.7 volts DC
Minimum input hysteresis = 0.2 volts DC.
Maximum input capacitance = 25 pF (measured at the device connector closest to the stub, if
any, within the device).
adaptec AHA-1740A/1742A/1744
1- 6

Electrical Interface for AHA-1744
As specified by ANSI X359.2/86-109 Rev. 10h for differential alternatives.
Output Signals
Each signal driven has the following output characteristics when measured at the
SCSI device’s connector:
Signal Definition Characteristics
VOL Low-level output voltage 1.7 volts DC maximum at IOL (low-level
output current) = 55 mA)
VOH High-level output voltage 2.7 volts DC minimum at IOH (high-level
output current) = -55 mA)
VOD Differential output voltage 1.0 volts DC minimum with with common-
mode voltage ranges from -7 to +12 volts DC
VOL and VOH are measured between the output terminal and the SCSI device’s logic ground
reference.
Input Signals
SCSI inputs meet the following electrical characteristics on each signal (including
both receivers and passive drivers):
Signal Definition Characteristics
IIInput current on either input +/- 2.0 mA maximum
Maximum input capacitance = 25 pF.
The IIrequirement is met with the input voltage varying between -7 and +12 volts DC, with
power on or off, and with the hysteresis equaling 35 millivolts, minimum.
Internal Connector
Unshrouded 50-pin header, compatible with unshielded alternative 1 connector as
specified in ANSI X3.131-1986 (Figure 4-1).
For connector pin out and drawing of the connector, see Appendix B.
Partial list of compatible connector plugs (for reference only):
Manufacturer Model Part Number
3-M N.A. 3425-6000
T&B Ansley N.A. 609-5000M
The cable for the internal SCSI connector should be good quality 50-conductor flat ca-
ble with 26- or 28-gauge conductors and a characteristic impedance (Z0) of 100 +/-10
ohms. Cable shielding is necessary if extremely noisy circuitry or extremely noise-
sensitive circuitry is present inside the host computer frame.
EISA-to-Fast SCSI Host Adapter Introduction
1-7

External Connector
Shielded 50-pin high density (Alternative 1) connector as specified in proposed ANSI
standard X3T9.2/86-109 Revision 10h, Section 4, Figure 5.
For connector pin out, see Appendix B.
Partial list of compatible connector plugs or cable assemblies (for reference only):
Manufacturer Model Part Number
AMP Connector 749111-4
Back Shell 749193-1
Fujitsu Connector FCN-237R050-G/F
Back Shell FCN-230C050-D/E or -C/E
Honda Connector PCS-XE50MA
Back Shell PCS-E50LA
Cable for external SCSI connector should be good quality 100% shielded round cable
with 25 twisted pairs. Each pair should have a characteristic impedance (Z0) between
90 ohms and 135 ohms. Wire gauge may be 26 or 28 AWG. All pairs should have the
same impedance and should have the same delay per length of cable. Cables meeting
these requirements will normally operate correctly in any SCSI configuration and
should normally meet all FCC requirements.
For best results, the SCSI committee recommends that SCSI connectors should not
be placed less than one foot apart on internal (ribbon) cable or on external cable
when using Fast SCSI 10 Mbytes/second data transfers.
Cable material which meets this specification is available from a number of vendors,
including:
Manufacturer Part Number Phone
C&T 16035
Madison 4099 [phone]
Complete cable assemblies are available from a number of manufacturers. Among
them are:
Manufacturer Phone
Amphenol Interconnect Products [phone]
Lynn Products Inc. [phone]
Quitec Interconnect Systems [phone]
Icontec [phone]
Enhance Cable Technology [phone]
adaptec AHA-1740A/1742A/1744
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