IBM SCSI /A
the IBM SCSI-1 Adapters
The old SCSI Adapter /A
Swapping BIOS chips for >1GB Support
Complex BIOS Levels for >1GB IML
Support (Type 1 and 2 ONLY!)
New BIOS Improvements
Multiple SCSI Device Order
The Short SCSI /A (>1GB support!)
OS/2 v.3 SCSI Controller switches
Unsure if the 44/45 SCSI bios will affect this.
The new short adapter is functionally equivalent to the
earlier full length version and the on-board termination scheme is the
same. The differences between the two cards besides the length are:
1. Short card firmware (Spock Prime) can handle the SCSI2 command
2. Long card firmware (Tribble) CAN NOT handle SCSI-2 Command
The SCSI /A long card will do 6.6 Mbps
° IBM Personal System/2 Micro Channel SCSI Adapter
The PS/2 Micro Channel SCSI Adapter
is a 16-bit Micro Channel bus master adapter that provides the ability
to connect multiple SCSI devices to all PS/2 Micro Channel systems. This
Micro Channel SCSI adapter adheres to the industry standard SCSI interface.
It features an 8.3MB per second burst data transfer rate, 16-bit data path
with 32-bit address capabilities, and can be installed in either a 16-
or 32-bit system card slot. A SCSI physical device could be a fixed
disk, scanner, plotter, printer, CD-ROM, or controller.
The bus master capability of this SCSI adapter
optimizes data flow from each SCSI device configured to the system. This
capability can provide performance benefits in applications where multitasking
or high-speed data flow is essential. It allows the processor to be off-loaded
from many of the input/output activities common to DASD transfers. This
SCSI Adapter also conforms to the Subsystem Control Block (SCB) architecture
for Micro Channel bus master.
Making Your Own IBM Cable
The actual cable itself is a standard SCSI-1 cable. The unusual
part is the 50 pin edgecard connector ( Dalco part 40720).
Note that Pin 1 on the adapter is towards the mounting bracket on the circuitboard
side of the adapter. (the pin on the component side is marked "2").
New BIOS Improvements
> Oh, really? Please expound on the "extra features" of the new SCSI
bios. In addition to handling drives >1GB as the IML drive, what else?
The upgrade provides the following additional capabilities:
1. More efficient use of Adapter ROM memory - minimizes adapter
2. BIOS support for fixed disks up to 3.94 gigabytes per device.
3. Supports "Search IML" from any PUN (Physical Unit Number)
SCSI ID. The system partition is no
longer restricted to only SCSI
ID=6. Each HD ID will be searched for
a valid system partition.
4. Allows redundant system partitions (IML).
5. Sharing of SCSI devices. An external SCSI device, such
as the 3511,
may be shared between two system units. The
menu item is "Target"
> So what good is the multiple, redundant partitions? Especially
with a T1-3 complex?
If drive id. 6 fails 'recovery' can be automatic
without the need to recover IML-capability by partially ripping the machine
down to change SCSI Id.s. You do, however, need to have planned for
this and set up the appropriate 'IML/Reference Partition'(s) and 'Active
Partition'(s) on the 'fallback' drives (Id. 5, 4, 3... etc.)
SCSI Device Ordering
Older SCSI adapters supported only a single bus which
provided both internal and external SCSI bus connectors for the single
bus. For these adapters, devices are logically ordered depending
only on adapter slot number and the SCSI IDs of the devices.
Now, i got 4-1gb 0662's w/cd-rom in my 9595-omt--
the problem is
this--win3.1 does'nt see all of these only 2 -0662's and cd-rom. Ref
disk sees all 5 w/cd-rom. I just added 2 0662's and not sure what's
them. I tried "fdisk" and "dos" but their not there. Any suggestions?
Scsi "id's" are as follows.
From Brad Parker
Using the ANSI/IBM standard, I would set the ID's as follows:
id 6 boot drive (c)
id 5 2nd hd (d)
id 4 3rd hd (e)
id 3 4th hd (f)
id 2 CD ROM (g)
Because the standard gives the greatest SCSI bus priority
to the highest
numbered drive and the lowest priority for the lowest numbered drive.
you have more than one partition on each drive, then the drive letters
change, but the device IDs will stay the same. In fact, I might just
the CD to id 0 to give yourself room for future expansion :-)
I have five HDs, three floppies, a 6 disc changer and a
Zip drive on one
of my 95s, of course I have two host adapters....
Maximum SCSI Devices Supported
Narrow SCSI devices support 8 possible SCSI ID values; therefore,
up to 7 narrow SCSI devices can be connected to the internal or external
SCSI busses in any combination using the remaining ID values. Wide
and narrow devices may be mixed on the same internal/external bus by using
the proper combinations of SCSI bus cables, terminators, and/or SCSI connector
Is the SCSI /A SCSI-2?
The SCSI adapter on the 8595 is "SCSI-2 compliant" - means:
it uses parts of the *command set* from SCSI-2 (command queueing, command
tagging) but the *transfer speed* is SCSI-1 with 5MB/s. It is also a "Narrow"-SCSI
controller - opposed to "Wide"-SCSI, which means it uses 8-bit devices
and not 16-bit devices.
However: it can handle even Ultra-SCSI drives, because
SCSI is compatible in any directions - other than shit-IDE.
And the controller is "Single Ended", which means that
every signal has GND as return line. "Differential" means, that every signal
has a return line with inversed polarity ... when -for example- +DATA0
sends a logical "1" on the active line the return line -DATA0 sends a logical
"0". The transceiver circuit in the device checks the *difference* between
the two signals (therefore "differential") - line disturbances afflict
both lines at once and are eliminated therefore.
Conclusion: the IBM SCSI adapter is 8-bit narrow, single-ended
SCSI with SCSI-2 style command set and SCSI-1 speed of 5MB/s. It can handle
7 Fast- or Ultra-SCSI devices and can handle even 7 Wide-devices if there
are converters used from Wide-to-narrow SCSI (68-to-50 pin) but these devices
must use device numbers from 0 - 6. The SCSI-ID 7 is used for the controller
itself. First device on IBM SCSI controllers is the one with the highest
ID (6) opposed to Adaptec or Buslogic controllers.
Controller And my favorite thing to see on
IBM PS/2 SCSI Adapter
Init file for _8EFE.ADF
Hmm, lookit the Oscillator values
8032-AH 10MHz microcontroller as
AIC-6250EL Line interface chip
ECA 032 Explanation
The old non-cached adapter can be identified by the FRU
15F6561on the lower left hand corner of the component side of the card.
Some adapters may have been updated.
The old card, Y1 is 25MHz and Y2 is 20 MHz. On the updated
adapters, Y1 is 20MHz and Y2 is 12.5MHz. Yellow wires may or may not exist
on any level of the card. If PN 85F0002 is present, it is the latest level
and does not need to be replaced. If you have either of these versions
of the 15F6561, replace them.
Joe Kovacs says
> The original IBm 32-bit SCSI (without cache) worked OK with HDs,
but lost bits with CDROMs. So an engineering change was specified,
and it was patched with a couple of wires in the upper right hand corner,
becoming an 85F0002..
The reworked 15F6561 cards I have seen have the rework
wires just about dead center (FAIR). Not sure if this is it...
Autotermination Capable Adapters or Planars
If the card or planar has a red colored T-Res, it does not have
the circuitry to support autotermination (you have to pull the termpack
if you add an external device). If the termpack is yellow, then the
additional circuitry exists and you can add or remove external devices
without having to pull the T-Res off the adapter.
> Peter, for the $64,000 Question. If you use a yellow termpack on a
adapter or board that had a red one initially, will that enable it
Definitely: No. The "Auto-Terminate" is a function that
require a little more hardware: a switching transistor that disables the
TermPwr wire from the T-RES and another transistor / IC function that senses
the voltage on the TermPwr line and the voltage on the data lines to figure
out whether the line is terminated or not.
From Tim Clarke
AFAIK, there is only one FRU for the "internal" termination
resistor pack for the IBM SCSI w/cache (adapter FRU 85F0063) that
has the appropriate 20-pin socket and the IBM SCSI w/o cache (adapter
FRU 85F0002). The termination resistor pack (20-pin) is FRU 57F2870
and, provided you insert it with Pin 1 correctly oriented, should work
Enable Termpower or Not?
Back in the "good old times" there was a fairly common
problem with the TERMPWR: if you had an external box and the device was
set to supply TERMPWR as well as the adapter it could happen that the external
device tries to feed back +5V via TERMPWR line into the controller once
the "computer" was turned off. Which often fried the cable and / or blew
the TERMPWR fuse(s).
The later standard defined the TERMPWR circuit as a "fuse
/ diode" combo:- the fuse (pico fuse or PTC / auto-reset fuse) to protect
the adapter / device against short-circuits on the TERMPWR line and the
diode to prevent backflow of +5V from external devices to the controller.
So *normally* there should be no problem to have TERMPWR
enabled on all devices - which makes sense on setups with very long cables
and multiple external devices. The importance of TERMPWR is often underestimated
in SCSI-1 environment. Here it is pretty important to feed the TERMPWR
line from *at least* one device to have the proper pull-up on the signal
lines at all. On SCSI-2, where each device *should* have its own active
termination and *should* monitor the TERMPWR and set the termination accordingly
it is of lesser importance. In the worst case one device supplies the termination
at least - if not the host adapter itself.
The main problem occurs, when the TERMPWR line on SCSI-1
setup is interrupted beween two devices and none of the devices supplies
TERMPWR: in this case a proper termination cannot be achieved, because
the (passive) terminator at the end of the chain has no TERMPWR to act
Multiple installed IBM SCSI MC/A (w/o Cache)
If more than one IBM MC/A SCSI Adapter (FRU P/N 85F0002
or 15F6561) is installed in a MC-System, and during setup two or more adapters
are shown with same PU/LU setup, or SCSI HD-drives connected to this card(s)
are not correct responding, check the EPROM's in position X5 (ZM5). The
EPROM-P/N in position X5 should be 41G9974.
Ed. Not sure what
this means. None of the SCSI Adapters I have use the mentioned EPROM. Good
Pinouts for the SCSI /A and the SCSI w/Cache
The edgecard for the SCSI Adapter /A has less contacts than
the later SCSI w/Cache. Still wondering why... But you can see a tableized
version (Thank you, thank you..) of Peter Wendt's observations. It is HERE.
The long, uncached adapter... This link is to an ECA that concerns a mandatory
Short SCSI /A
The uncached SCSI adapter was available in two different versions as
well: the long card, which cannot handle >1GB and the short card (half
card with microcode dated 1993 and later) which can.
|J1 Internal SCSI Header
J2 C60 External SCSI Port
U2 92F2245 SCSI BIOS Odd
U5 54G1800 512K
U7 92F2244 SCSI BIOS Even
|U8 Intel 80C32GBAA
U9 84F8324 Line Interface
U15 CXK5864BM-10LL 8Kx8
RN1 Bourns 4120R-003
RT1 Bourn 100 HG9K
Y1 20 MHz
Y2 25 MHz
80C32GB- 10MHz microcontroller as
J3 Serial Port
Made up name. This is a status link header like on the
late SCSI w/cache. From left to right, the pinout is CHR, ITS, BRN, TXD,
T-Res for Short SCSI/A
I finally got two primo condition short SCSI/A controllers.
They both have a yellow termpack, Bourn 4120R-003 -221/331. This means
they have autotermination.
The short card has been built by IBM to fulfill longer
running service contracts on old machines after production of the long
uncached adapter ran out. The BIOS is located top / left, two small chips
with 92F2244 and 92F2245. These are the same P/N as used on the "later"
cached SCSI Adapter and already contain the upgraded code for IML
drives up to 3.94GB. The adaptercard itself is an interesting mix of components
from the uncached (long) and later cached (long) SCSI adapters. Works nicely.
Swapping BIOS chips
for >1GB Support
From Peter Wendt
Some time ago Charles Lassiter sent me one of the rare
short IBM SCSI adapters without cache /A ... and I found out, that this
adapter uses the same two SCSI-Bios chips 92F2244 and 92F2245 as the "later"
SCSI adapter with cache. This card however is a strange mix of this "later"
adapter and the uncached ... on half the length.
Today - while juggeling around with parts & cards on a Model 90
- I decided by what reason to remove the SCSI-Bios from an old uncached
SCSI and stuff that from the "later" cached on it. Earlier this year I'd
tried to swap the entire Eprom-Sets among the old and the later cached
- and it did not work. Today I left the busmaster microcode Eprom on the
card and only swapped the SCSI-Bios.
To my undescribeable surprise: it worked.
To make sure that it is not a gimmick of that machines' Bios
I tried it on a Mod. 70-A21, which has definitely no enhanced SCSI-Bios
support in the planar microcode. I pulled the 2GB IBM 0664 harddisk from
my WinNT Server and installed it in the Mod. 70. I have a heavily modified
Mod. 70 - has a standard power-plug (as described on my page, folks !)
and a Kingston 486DX-33 upgrade. I also installed the uncached SCSI with
the old Eproms. No surprise: "No operating system" and the system halted.
Then I used the 92F2244 and 92F2245 on that same adapter ... Voilà:
"OS Loader V4.00 ..." and WinNT 4.0 Server started up ... ! (Ever seen
that on a Mod. 70 ?) Tried the same procedure with the old IBM SCSI adapter
with cache (the one *with* the AIC-6250EL Line Interface) - with the same
results. Old Bios-chips: No operating system - New chips: Win NT
Conclusion: If you have one of the older SCSI-Adapter *cards* you can
use the SCSI-Bios from the later-level SCSI Adapter with cache to make
the system capable to handle drives over 1GB.
I do *not* know if there is another limit after 4GB - but assume it
is (I don't have drives over 2.2GB currently). This limitation will at
least exist on the IML-machines, since the principle that starts up the
IML cannot handle drives over 3.94GB (the mysterious IML-border) due to
the technical method of putting the systempartition MBR at *the end* of
the physical diskspace. The register width is obviously limited to any
number of total data-blocks below 4GB. So that does not change at all.
Upgrade Needed for >1GB IML Drive
From Tim Clarke
After an extended E-mail exchange with Al Brandt, who
couldn't get a machine to IML from a >1GB drive (SCSI ID. 6) attached to
a SCSI-1 controller w/cache but with the notorious (now infamous?) 92F2244
and 92F2245 'Enhanced SCSI BIOS' ROMs using a Type-1 complex with either
of the 'older' complex BIOS ROMs (i.e. 84F9154 for SOD Type-1 and 91F9812
for non-SOD Type-1), I decided to run my own tests.
'Enhanced IML' in the complex upgrades is the *only* way
to be able to IML from a drive >1GB (and from a drive Id. ¬= 6).
At this time I must assume that the 92F2244+5 ROMs provide
support for drives <= 4GB, but the 'old' complex ROMs' IML support somehow
does not make (proper) use of it, possibly due to bad bit-shifting and/or
masking when 'translating' the 'cylinder, head, sector' information to
and from the SCSI 'logical block/sector' value.
From another thread
BTW, space is usually allocated as a whole no. of
cylinders, so the 'old' 3MB "System/Reference Partition" will grow to ~12MB
on a >1GB drive.Albeit that only the 1st 3MB of that space is used/needed.
Some Other Thoughts
From Charles Lasitter
I've had some VERY entertaining results in my installations,
depending on what other drives were present, and which version of the processor
BIOS was used.
With the 52G9509 in place, ID6 in bottom bay (Mod 95)
at end of cable, ID5 in bay above on next spot on cable, I couldn't get
the IML to go to ID6 to save my ass. It made a beeline for ID5 every
time. Put in the old BIOS, and it goes straight for ID6.
I think there are a LOT of quirks like this (and yours)
to be mapped out, and that seemingly innocuous settings changes in the
ABIOS make differences you'd never guess sometimes.
I also suspect that the Mod 90 is it's very own distinct
bird with it's own eccentricities in this and related matters.