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Introduction
Flash-based Systems
Supported Flash Devices
Model 85 "X"
Model 85 "K/N"
Model 76/77 i/s "Lacuna"
Model 90/95 Type 4 Complex
Content by Major Tom. Last update: 19 Nov 2023
Introduction
Most late PS/2 systems use Flash memory to store the system firmware
(POST/BIOS). This type of memory can be erased and reprogrammed "on-the-fly" by
the system CPU, making BIOS updates much easier than in the earlier systems
that required replacement ROM chips or reprogramming in a standalone
programmer.
Flash chips from the same family are compatible as far as read operations
are concerned, different members of the family will however have a unique
identifier, and may use different programming protocols. The flash routine
stored in the system BIOS only recognizes a few selected identifiers and
supports only the corresponding programming protocols. Therefore it's important
to use one of the supported parts when replacing defective flash chip(s), if
you want to retain the flash update functionality.
Below is a list of supported parts for all flash-based PS/2s. Two identical
parts are required. The information provided here is based on the latest
available BIOS code (YMMV if you use some older revision).
Note: I'm not certain whether it's possible to
directly replace 12 V parts with 5 V parts or vice versa. More investigation is
necessary to see if the programming voltage is fixed (set by soldered
resistors/jumpers) or software-controlled.
Note: The flash chips come in a surface mount
32-pin PLCC package, and are typically soldered directly to the PCB (planar or
complex)! So some skill and ideally a rework station is required to replace
these. Be careful out there...
Flash-based Systems
Supported Flash Devices
The programming support (erasing and writing algorithms) for the compatible
flash devices is stored within the system firmware itself. The flash update
utility uses the Int 15 interface to invoke these routines.
Below is a list of flash devices supported by the different system planars.
Not all devices were actually used in production.
Model 85 "X"
| Mfg. |
Type |
Size |
Part Id (hex) |
Prog.
voltage |
| Mfg. |
Device |
| Intel |
28F010 |
128 KB |
89 |
B4 |
12 V |
| AMD |
Am28F010 |
128 KB |
01 |
A7 |
12 V |
Model 85 "K/N"
| Mfg. |
Type |
Size |
Part Id (hex) |
Prog.
voltage |
| Mfg. |
Device |
| Intel |
28F020 |
256 KB |
89 |
BD |
12 V |
| AMD |
Am28F020 |
256 KB |
01 |
2A |
12 V |
Unlike all the other flash-based PS/2s, the "K/N" has 2 x 256 KB of flash
memory.
Model 76/77 i/s "Lacuna"
| Mfg. |
Type |
Size |
Part Id (hex) |
Prog.
voltage |
| Mfg. |
Device |
| Intel |
28F512 |
64 KB * |
89 |
B8 |
12 V |
| AMD |
Am29F010 |
128 KB |
01 |
20 |
5 V |
* This one is suspicious. 2 x 64 KB is not enough to store the SurePath
BIOS. Both my Lacunas come with the Am29F010 chips. Needs more digging to see
what's going on here.
Model 90/95 Type 4 Complex
| Mfg. |
Type |
Size |
Part Id (hex) |
Prog.
voltage |
| Mfg. |
Device |
| Intel |
28F010 |
128 KB |
89 |
B4 |
12 V |
| AMD |
Am28F010 |
128 KB |
01 |
A7 |
12 V |
| ST |
M28F101 |
128 KB |
20 |
07 |
12 V |
| TI |
TMS28F010 |
128 KB |
97 |
75 |
12 V |
| AMD |
Am29F010 |
128 KB |
01 |
20 |
5 V |
The older Type 4 processor boards - "N" and "P" have a local DC/DC converter
that is used to generate 12 V programming voltage (Vpp) that is required by
some flash chips. The board should support all parts listed in the table above,
including the 5 V Am29F010 part. (It has the same pinout, but pin 1, that is
normally used to supply the programming voltage, is unused here.) It's however
unlikely that any of these older boards came with 5 V Vpp flash chips.
The newer boards - "Q" and "Y" don't have a local 12 V generator. Therefore
they won't be able to flash parts that requite this higher programming voltage.
Only the 5 V Am29F010 (or 100% compatible alternative) is supported by these
boards.
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