You're never going to find a datasheet for anything PCchips. Might as well forget about it.

If it is indeed based on an OPTi 495, that would be interesting however. There are at least four different versions of the 495 chip. Typically with each version of the chipset, they will reduce the chip count (integrate more crap).

I know of four versions:

-495
-495SLC
-495SX
-495XLC

The original 495 is the least integrated, and the 495XLC is the most. The original 495 is pretty uncommon, and I've only ever seen it on older full length 386 boards. The 495XLC is the most integrated, and it's found almost exclusively on those tiny half length 386 boards.

If your board uses a 495 type chipset, it's probably either an SLC or SX. As far as I know the only difference between these two is buffered vs unbuffered VLB slots.

Which 495 manual do you have?

The comparison i did was with 495XLC datasheet. I'll try to find others and compare the registers with them as well.

Thanks!

EDIT: The SX, SLC and XLC seem to be one-chip chipsets, if i didn't miss anything by looking all kinds of motherboards with 495 chipset. That only leaves an option for old 495, as my motherboard has 2-chip chipset...

I daily use a M321 board to navigate the Internet with Lynx and Links. Excellent board, more than 25 years of use without a single problem.

The M-321 80386 Mainboard User's Guide gives as one of it's Key Features:
Synchronous AT bus clock with programmable clock (divided by eight).
It also states that:

Syster Timer:
The Counter/Timer (CTC) is located in the 82C206 IPC ....
and a long description of how it works, the 6 Modes of operation, the three 16-bit counters, etc.
In my M-321 REV 2.5 the chip is a PCCHIPS C206 242
In my M-321 REV 2.6 the chip is a PCCHIPS 16329 245
both at the end of the 8-bit expansion slots.

........
Synchronous AT bus clock with programmable clock (divided by eight)

I have the REV 2.6 variant.

So it should be possible to change the divider? (/8 is awful! It's 5MHz!)

Probably, divided by 8 means with respect to the 80 MHZ crystal oscillator ===> 10 MHZ bus..

The M-321 Mainboard User's Guide gives no instructions on how to change the divider.

None of the 495s are single chips. The original 495 should be 3 chip. 495SX seems to be 3 chip as well, and the SLC and XLC both appear to be 2 chip.

I suspect the 495, 495SX and 495SLC are all register compatible, but the XLC may be slightly different.
The reason I suspect this is that the XLC MR-BIOS doesn't seem to work well in my 495SX board.

Alejandro Lieber wrote:

In my M-321 REV 2.5 the chip is a PCCHIPS C206 242
In my M-321 REV 2.6 the chip is a PCCHIPS 16329 245
both at the end of the 8-bit expansion slots.

I have a REV 2.6 with C206 chip. 😖

As in, an in an 82C206? Almost all 386 boards (except for the fully integrated ones) have those. They come from many different sources and are interchangeable. Sometimes you'll find an OPTi board with a UMC branded 82C206 chip, but it still counts as part of the chipset. In the case of these M321 boards, the chipset consists of 3 chips.

Anonymous Coward wrote:

As in, an in an 82C206? Almost all 386 boards (except for the fully integrated ones) have those. They come from many different sources and are interchangeable. Sometimes you'll find an OPTi board with a UMC branded 82C206 chip, but it still counts as part of the chipset. In the case of these M321 boards, the chipset consists of 3 chips.

Yes, 82C206.

I still have yet to find the 82C495 non-XLC chipsets datasheet with register information... If somebody has it laying around, that would be great. 😁

I think I might have the datasheet for one other 495 chipset. Possibly 495SX or SLC. I'll have to check my desktop PC harddrive. A lot of datasheets are online, but they're hard to find because they have stupid names.

I've got a M321 Rev 2.5 motherboard and cannot get it to boot off hdds. I've tried numerous hdds with standard ide interface cards, including Promise EIDE card and scsi controllers. It just freezes when it tried to access any hdd. Floppy seek works but it also refuses to boot from floppies. Bios settings are correct, ram and cache working fine. Even tried xt-ide on nic with normal IDE hdd interface card and it hangs trying to access the hdd. Anyone have a jumper layout of this mobo? Current setup AMD386DX/DXL-40, Cyrix FasMath co-pro, 128k L2 cache, 8megs of ram, various hdds ranging from 128megs up to 2gig. Some drives were freshly set up on a 486. Even tried hdd with drive overlay overlay software. Swapped out cpus and co-pros. CMOS battery is fine. Run without co-pro same result-no boot. Also doesn't respond to ctrl-alt-del when frozen, needing a hard reset. I've spent way too much time on this.

Everything works fine on a 486 board I've got. All hard drives boot, SCSI and Promise cards work as they should.

Any advise would be appreciated. Thanks

Sorted. Disabled the L2 cache and it booted fine. I'm sure I tried that yesterday. Oh well I guess having a fresh start helps.

Old thread resurrection but PC Chips m321 should be based on 82c391/82c392/82c206 Opti-386WB Chipset, here is the datasheet for future reference. The Bus divider options are clk2in/8 or clk2in/6, so with an am386dx40 (80 Mhz crystal) and the 8 divider the actual isa bus is 10Mhz. Input PIN 14 (BCLKS) of 82c391 selects the multiplier, if low clk2in/8 is selected, if high clk2in/6 is used.
IC marked CHIP 5 is the 82c392 while IC marked CHIP 6 is the 82c391.

How do you know ? Can you test the m321 with a bios for that chipset just to make sure ? ^^

Great! This document has register bits information too. I'll try to make some time to match those with my motherboard and maybe change some wait states and check the benchmarks then. 😉

GigAHerZ wrote on 2020-10-01, 06:41:

Great! This document has register bits information too. I'll try to make some time to match those with my motherboard and maybe change some wait states and check the benchmarks then. 😉

Interesting! Keep us updated.

Deksor wrote on 2020-10-01, 05:58:

How do you know ? Can you test the m321 with a bios for that chipset just to make sure ? ^^

If you hex edit a m321 rev.2.7 bios dump you will find references to 82c391/82c391b, regarding the ISA Bus dividers: "This is valid only for 82C391B Chipset. The options are: -Jumper : AT Bus Clock is CPU clock input divided either by 6 or by 8 determined by hardware jumper. CLKIN/10 : AT Bus Clock is CPU clock input divided by 10. For 82C391 Chipset, this is "Reserved"." take a look, in my dump this is at OFFSET BC3F . The layout also fits and from a pictures analysis also the chipset connections. As I said it should be based on that chipset. I could be mistaken ofc. Sadly I don't have the mobo, so someone else should test the bios on his board. There is a Mr.Bios for it, I will post it here.

-------------------------------------------------
OPTi WriteBack 82C391 / 82C491 / 82C493 / 82C495
-------------------------------------------------

NOTICE: 386: Beginning Ver 1.40, Dirty-Bits are optional, all cache sizes.
493/5: Beginning Ver 1.41, Dirty-Bits are required only with 512K
cache. 64K, 128K, 256K may omit Dirty-Bits.


Filename Port Description (386-WB Revs A,B)
-------- ------- ---------------------------------------------------------
V020B324 OPTI324 82C391 - 386 WriteBack Revs A,B
V020B32B OPTI32B x020B324 with C&T 82C711 multi-IO
V020B32C OPTI32C x020B324 with NSC PC87310 Super-IO

V020B32E OPTI32E x020B324 (T-)
V020B32F OPTI32F x020B324 (T+)
V020B32G OPTI32G x020B324 (CL-)
V020B32H OPTI32H x020B324 (CL+)

V020B32J OPTI32J x020B32B (711) (T-)
V020B32K OPTI32K x020B32B (711) (T+)
V020B32L OPTI32L x020B32B (711) (CL-)
V020B32M OPTI32M x020B32B (711) (CL+)

V020B32P OPTI32P x020B32C (310) (T-)
V020B32Q OPTI32Q x020B32C (310) (T+)
V020B32R OPTI32R x020B32C (310) (CL-)
V020B32S OPTI32S x020B32C (310) (CL+)