AT27C256R-15R 28 pin SOIC BIOS and firmware
Indicator Port Pinout (J17)
Failing Planar? Bad caps
Slot Numbers and Widths
Remove SCSI BIOS Chips
SCSI and System BIOS Wondering
Set SCSI ID
Filling SIMM Sockets
64MB in a P75?
Actions On Memory Errors
Attempting 2.88MB Support (Always use the stock refdisk!)
Undorking a P75
External Storage Device Connector
External Storage Device Cable Source
Remove Floppy Drive (H1 Model)
Reassemble Floppy Drive
P75 Drive Carrier Screw Spacings
P75 HD Rail Dimensions
Hard Drive Mounting Rails
Hard Drive Mounted in Cage
P75 CMOS Battery Replacement (Dr. Jim)
Dr Jim Shorney's P75 Processor Card Mods (local copy, archived version HERE)
J1 and J2 Function
Blank Plasma Display (14902 Error or just no video at all)
Active Matrix LED Screen Prototype
Riser Swap with P70
Built-in Features ADF
P75 Planar 78F9896
90X8134ESD, just like on the K and 0 complexes and the 50Z planar.
J17 six pin header for floppy drive, power, and hard drive LEDs
J20 MC-2 14 pin header that connects to riser card.
J8 Wire Colors
Numbers and Widths
Slot 4 (Outer Top) 32-bit AVE
Memory expansion cards in Slot 2!
To me, it resembles the newer SCSI /A with the 20MHz/12.5MHz oscillators.
P75 SCSI Tribble (new)
80C32-1 CPU N8032AH
20000 xtal KHz? 20 MHz
12500 xtal KHz? 12.5 MHz
OKI 15F7917 OKI 15F7917
Take a look at David Beem's SCSI microcode levels. The latest ucode for the Tribble is
41G9974 14h/20d date 1992.
Atmel AT27C256R-15R 28 pin SOIC [package 28R] BIOS and firmware
Package Type R - 28 Lead, 0.330" Wide, Plastic Gull Wing Small Outline (SOIC)
SCSI BIOS PN 79F3214 (even) / PN 79F3213 (odd). SCSI microcode PN 79F3212 Ed. I had Bruce from Blue Feather Technologies burn me some of the 92F2244 and 92F2245 SCSI BIOS in the small SOIC chips and use them in my P75s. Up to six SCSI devices can be attached to the SCSI controller. It supports drives up to 1.05GB.
Dr. Jim says:
At first I tried using a 2.1GB Quantum Fireball attached to the onboard SCSI controller. The drive was properly recognized with 2.112MB in the setup - but it did not show up with the proper capacity in FDISK. I tried Win95 FDISK - which showed a size of 1.024MB (1.0GB) as estimated even with the advanced large media support turned on.
Then I installed the short IBM PS/2 Fast SCSI-2 Adapter /A (60E9) in the second lower 16-bit slot. The first slot contained a short 16/4 Token Ring adapter already. While the card has no front tab it just fits between the rear slotcover and the power supply fan without squeezing :-) A very tight fit if you ask me. The internal SCSI cable could be detached from the planar SCSI port and attached to the SCSI-2 card. The length is sufficient.
Now: this seems to work.
It is however not possible to configure the SCSI device(s) attached to that controller, if you only copy the ADF to the reference disk. Most likely you will have to use "copy an Option Disk" and get the updated SCSI.DGS, SCSIHF.DGS and -probably- SC.EXE to the P75 reference disk. I did not do that ... so far. Maybe later, because I only have a US-P75 reference and only a german "SCSI-2 Option Disk" - and if there is one thing how to voluntarily step in the mud then it is mixing different language versions.
The P75 also lacks the ability to select the startup sequence - but at least it had no problem determining that the planar SCSI only has an external CD-ROM attached and that the 2.1GB harddisk is on the SCSI-2. FDISK got straight through and installed a 2GB primary partition. After reboot the FORMAT C: says "Formatting 2.012,03MB" ... which takes a while, because this particular drive has some bad sectors, which are not hidden. Strange. But okay.
Physically the slimline Quantum drive fits into the half-height HD-cage. But the ID-select cable has an "old raster" plug for the large jumper pins, while the Quantum has the "mini jumpers", which are thinner and have only 1.5mm pitch. Doesn't matter much, because once set there is no reason to have the drive ID switched to anything else than the pre-set ID 6 (traditionally I took ID-6 of course).
Sadly the P75 has a soldered firmware ROM on the processor card. There is no chance to read out the ROM content *after* the system powered up - and then the ROM is relocated to an area above 16MB and masked from access. Only the shadow-copy remains at the addresses E000 - FFFF and is mixed with the additional codes from the XGA and planar SCSI.
This is the same method as used on all PS/2 with 486-class processors (and even 386 CPUs) - but these have removable ROMs that could be read and analyzed before the POST relocates the "pure ROM code" out and only the "compatibility part" remains. I would really like to compare e.g. a Type 2 (old) and 41G9361 Type 2 (new) code for the advanced SCSI support and try to add this to the P75 firmware ROM, which *seem* rather close to the Type 2. Technically the P75 is a sort of Mod. 77 / Mod. 90 mix in a portable case. It has a similar memory subsystem (single modules, unpaired) and the planar SCSI from the "Bermuda" 77, it got the planar XGA-1 from the Mod. 90. So either of these machines -to my opinion- could be used to filter out the additional code that enables the planar SCSI controller to handle drives over 1GB.
On the Mod. 90 the code can be supplied with the
upgrade version of the the processor board firmware ROM
- why not on the P75 ?
Anyone any idea to this ? I don't have
the equipment to unsolder the SMD-ROM undamaged or read
it out. My Eprommer takes only DIL-chips ... but that is
the least problem, because I can build / buy an adapter.
The ROM itself is a 27C1001 / 27C010-version (128K x 8
bit) as far as I remember ... I have PLCC 28C010
Flash-ROMs around here ... :-)
Hey Jim - wouldn't that be another
challenge to push out the P75 performance a bit more ?
The advanced SCSI support on the Mod. 77 "B" helps it to
even run 8GB drives .... tried that with my old
Ultimedia-77 and a Seagate Elite-9 drive, before they
were installed in the 9585. No problems getting them to
work under NT 4.0.
Set SCSI ID
SCSI connectors have the pin holes facing UP. The length
of the flat and loose is immaterial, but the OAL should
be AT LEAST 6.5". The end for the drive should use a
2 and 4MB 70nS parity SIMMs are supported, max 16MB on the planar.
Panasonic OEM (IGH0380BA)
4MB is FRU 64F3605 P/N 64F8776
64F3605 and 92F0105
Thinkpad General - Model P70
And P75 Memory Checkout
64MB on a P75
Ivar Amund Grimstad wrote:
I have upgraded to a total of 64MB RAM, using 12MB on the planar and 52MB on a Kingston KTM-MC64 expansion board that fits only in the upper 32-bit slot. (Ed. I think there has to be a "memory window" in the 16MB so you can "map" the extended memory into it. Might be able to get 14MB on the planar with 4x4x4x2?) (Ed. Slot 2 is the MME slot)
That's right. The P75 is -more or less- a
"Model 90 with a carrying handle". So the 16MB memory
limit does not directly apply on that machine (unlike to
Mod. 70 and 80). However: the planar memory mapper seems
to be a bit odd and needs to map in the memory on a card
("Channel Memory") into the lower 16MB to have it
addressable. That's why I had to remove memory from the
Interesting in this respect was the fact
that I had to remove 4MB when the Acculogic was equipped
with 4 x 4MB modules and I had to remove 8MB from the
planar, when it had 4 x 8MB. Seems as if the memory
granularity only adjusts to full module values (4 or
Action on Memory Error
The P75 allocates memory in 2MB blocks, except for the first 2MB of system-board memory. For errors in this first block, the following occurs:
Error in First 512KB
Error Outside First 512KB
If errors occur one at a time, the system
deactivates 2MB blocks of memory. However, if two errors
occur at the same time on the same SIMM, the system
programs cannot be loaded and an error message is
The floppy can be used in the open or closed position. It is recommended that it is operated in the closed position so the chance of foreign material dropping in the drive is greatly reduced.
The floppy in my P75 is a ALPS DFP723D15C, 12v .47A, 5v .16A
Using the 2.88MB Floppy
According to the Western Gunslinger, David Beem, the non-star 2.88 works. So I whipped out a FRU 64F4148, Sony MP-F40W-03, and dropped it in with some trepidation.
model has the same layout as the original ALPS
DFP723D15C. Looking from above, the drive motor is on
the left (same side as the eject button) and floppy
cable is on the right.
Note: After some
thought, the cable tie holding the floppy cable to the
bracket on the PSU is most likely to assist in
positioning the floppy header during assembly. It is
possible that carefully cutting the cable tie would
allow you to use a 2.88MB floppy with the 34 pin header
on either side...
Just swap the plasticized shield to the new drive (nice that the big exposed flywheel is gone on the 2.88), and put on the rails. Because of the black dust shutter, you can't just slap on those rails. Instead, start the rear screw first. Now pull out on the front end of the white rail and start the front screw. Now you can snug it down with little trouble.
Longer 2.88MB Eject Button
Refdisk for 2.88MB Support
The problem is when you hose the POS values with the bogus refdisk, the stock refdisk WON'T WORK! Worse, it comes up as a Non-System disk. Tim Clarke is of the opinion that the later refdisks move the extended CMOS area, and that's what sends the floppy to Nirvana.
This was more fun than being attacked with a Ronco Turnip Twaddler... I was unable to reset the CMOS with any utility that I tried, the floppy could read the floppy, but trying to open files produced Disk not Ready errors.
I noticed that I could boot with a PC DOS 7 boot disk, so out of hope (desperation?) I created a PC DOS 7 bootable floppy, then dumped all the other files (minus command.com, ibmbio.com and ibmdos.com) to the boot disk. I then used Bob Eager's REFSTAMP on it.
The hybrid refdisk will boot to the PC DOS prompt. I then ran SC.EXE from the command line, configured, then saved it. Sort of nice with the bootable floppy, as soon as you hit F3 to exit, it returns you to the command line. Run SETCLOCK.EXE to set your clock.
Shorting the MC146818AF RTC
With power off and the battery unplugged,
short pins 12 and 24 together for 15 seconds. That's the
certain way to clear it, yet I am not totally convinced
it clears everything.
Pin 1 on the RTC faces left, so 12 is the rightmost pin on the bottom, and pin 24 is the leftmost pin on the top. (Thanks to William Walsh for sending a snippet from the newsgroups).
Stick the MCA slot bracket back on, replace all screws and posts.
Boot with the PC DOS 7/refdisk hybrid. Run SC.EXE and
SETCLOCK.EXE, now the system should (maybe, possibly)
External Storage Device Connector
Shared with the P70, look HERE
Continue to rotate it until
it is level, then pull it straight out.
Removing Floppy from Drive
Carrier, H1 Model
Unscrew both screws from the upper side of the
carrier. Pull the floppy rearward until the white
plastic piece on the right side is just to the front of
If you look into the recess that the drive carrier fits into, you will notice a black catch in the upper right corner. Now look at the two white plastic pieces. Notice that one has a little "arm" sticking up? This part gets screwed on the floppy on the same side as the eject button.
Slip the left side of the floppy into the drive carrier. Pull the right side of the carrier out so the floppy "rail" will clear. Slide drive forward until it stops. Install both self tapping screws.
There is a aluminum ground shield across the bottom of
the floppy drive. It is attached with four screws
through the bottom mounting holes (which are not used by
the plastic "rails"). It is coated on one side with a
plastic non-conductive coating. To properly attach this
shield, the grounding strap "tab"
MUST be on the same side
as the motor! A simple test- use an ohmmeter on the
shield, one side conducts, the other, not.
P75 Drive Carrier
My vision: Get a angle bracket, cut to length, drill
mounting holes in the top and sides.
P75 HD Rail
Note: The distance to the angle for these holes is not critical, as long as you have clearance
for the screw heads.
First hole for the HD to rail is 2.375". second hole is at 4.125". Both holes are .125" from the angle
Note: These holes MUST be .125" away from the angle, since the Hard Drive width can't change...
Note: The rails are
mirror images, they are NOT identical!. The dimensions
are the same, but swapped.
The HD mounting holes are .125" from the edge of the angle, and interfere with installing the screw, so I used a keyway cutter to mill away a slot to give the screw head clearance. The holes to mount the rails are 5/32 for now, but I'm thinking of switching to a mild steel angle because the extruded aluminum is soft. I could have tapped it for 10/32, but I'm afraid that it would be too easy to strip the threads from aluminum.
P75 HD Cage with Drive Rails
Here's a shot with the drive on the rails. I used 3/8ths inch 8x32 nylon machine screws and nuts from Ace Hardware. The nylon screws were a close fit in the 5/32" holes, almost like a barbed fastener... You might just stick with 5/32 and nylon screws for a quick assembly. Note: The aluminum angle used may make "shavings" when threaded for use with steel screws. Consider threading for 8x32 and use nylon screws...I wonder if a thread forming tap would work.
Using aluminum is OK, but be careful of threading.. Use the same diameter drill for all holes if you can. Use a 1/2" diameter by 3/16" wide keyway cutter. A .750" dia cutter leaves too much flash.
If you use an ER-20 collet chuck, get a 3/8" shaft keyway cutter so it fits...
Battery Pack PN 79F3198 (assembly) Battery Card, PN 64F8794
The P75 uses a 6V battery pack, with two Panasonic CR2477 3v 1000 mAh cells in series soldered to a circuit board.
The battery header (J18) is a four pin header with one pin missing. The plug on the end of the battery card cable has one position plugged.
Processor Card PN 64F8775 FRU 64F8789
Shorney's P75 wizardry" Images
Video Card PN 78F9895 FRU 78F9897
A lot of these are used on the XGA adapter.
and J2 Function
* Storage position
Similar functions may also apply to those on the P70
video display adapters, possibly modifying the VGA
adapter ID (EFFD) in a similar manner.
To install Brightness program, run Brtinst.com from the refdisk. This installs brt.com.
To have emphasized text brighter than standard text, type "BRT" and press Enter. To have standard text brighter than emphasized text, type "BRT /H" and press Enter.
The P75 has XGA-1 with 1MB VRAM.
The internal display however supports only the 640 x 480 mode and turns off if any of the higher modes is used. This will explain why you can get a picture on the external screen but not on the plasma.
You will have to stay at the low-res mode here, since the display is from the principle only a "generic VGA screen" (same as on the P70 BTW).
Type "P75/u" at dos prompt (undo) option to return to
the monitor connected to the XGA2 Adapter.
Matrix LED Screen Prototype
"IBM Rolls Out 22-Pound, 486 'Luggable'
As part of the announcement, the company last week
demonstrated a flat-panel color display it jointly
developed with Toshiba. However, IBM officials declined
to say if it would be available for the P75. The color
display is scheduled to be delivered in the first half
of 1991, IBM officials said.
Course: IBM’s Strategic Recovery in the Flat Panel
The big move came in 1986 when IBM entered into a
two-year joint research alliance with Japanese
manufacturer Toshiba focused explicitly on full-color,
active matrix (AM) LCD TFTs. IBM initially considered
other partners such as GE, Sharp, Matsushita, and
Hitachi but settled on
The relationship initially focused on proving that the
smaller (2”-3”) LCD televisions could be effectively
scaled up to larger sizes, and then moved to the
creation of a 14” full color prototype computer display.
In 1988 the two firms signed a joint venture agreement
to create Display Technologies Inc. (DTI) and build a
manufacturing facility in Himeji City in Japan next to
an existing Toshiba monochrome LCD plant. By 1991, DTI
had created the monitor for the P75 portable and in 1992
for the first IBM ThinkPad. In 1992, DTI produced around
500,000 TFT panels for use by IBM and Toshiba, as well
as for sale to other companies.
Riser Swap with P70
Gee, ever think of using a P75 riser on a P70? Well, it doesn't look good- The riser may fit, but the P75 has a 14 pin header from the board to the riser card. Of course, the P70 lacks it entirely. Probably the extra control lines? Whatever. Another MAD fantasy...
Win98SE on P75
Today I have tested my trusty old "PortaPotty" 8573-401 (P75 Luggable) with Win98SE. My configuration: unmodified 486DX-33, 8MB (2 x 4) on the planar, 32MB (4 x 8) on the Acculogic Simmply Ram, Madge 16/4 TR (Tropic chipset), Maxtor MXT540S at SCSI-ID6, external CD-ROM II (caddy loaded) in 3510-AV0 enclosure.
Win98SE install took about 3 hours ... I went away in between for lunch and missed to "press any key". The system hung at one point prior to the first reboot after the files had been copied from the CD and before you are asked to enter the 4 x 5 ident characters. I switched the machine off and powered it back on. Caused no major problem except waiting for the 40 Megs RAM to count up.
Result (after that long time): "Your system is optimal configured". No 16-bit mode, full access to the CD-ROM etc. pp. ... but it is rather slow. Guess I'll have to send in the processor board to Doctor Jim for some supercharging ... :-)
P75 System ADF 0E0FFh AdapterName "Built In Features"
Serial 1 through Serial 8, or disabled.
<SERIAL_1 03f8-03ff int 4>, 2 (02f8-02ff int 3), 3 (3220-3227 int 3), 4 (3228-322f int 3), 5 (4220-4227 int 3), 6 (4228-422f int 3), 7 (5220-5227 int 3), 5 (228 -522f int 3), Disabled
Parallel Port Arbitration
Video I/O Address
Video ROM Address Space
Video Arbitration Level
Color to Gray Mapping
Content created and/or collected by: