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Upgrading a 386SX - some advice!

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First post, by Spirantho

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Hi,

I noticed this morning a thread (which I now can't find) about switching a 386SX CPU, so I thought I'd share my knowledge and maybe save other people the hassle I've been through.

Some points:
The 386SX chips are all - more or less - the same, be they Intel or AMD or whatever.
The 486SLC chips are different. There are two cores:
The Cyrix core is different to the IBM core, which is faster.
The Cyrix chips have 1KB cache, the IBM has 8KB, at least on the faster chips.

Be careful! If the code on the chip has a "V" in it, it's a 3.3V part! To switch with an SX, you need 5V. So:
Cx486SLC/e-25 = good! This is a direct replacement for a 386SX!
Tx486SLC/c-25 = good!
Cx486SLC/e-V25 = bad! This is a 3.3V part
Tx486SLC/e-V25 = bad!

Now, if you want real speed, you need a clock-doubled part. You can find these on clip-on accelerators, but they can be a bit unreliable.
Essentially, you need to see if the clip-on chip has a daughterboard with a voltage converter on it. If it does, it's no good.

Cx486SLC2-50MP = good! 50MHz power! This is the fastest I've found yet.
Tx486SLC2 = beware! I believe these are 3.3V parts!
IBM 486SLC/2 and above = all (doubled?) IBM parts are 3.3V! These are not direct replacements.

In other words:
Tx486SLC/e-xx, Cx486SLC/e-xx and Cx486SLC2-xxMP are all good, with the latter being the fastest.

There may be others, but if you want to upgrade your 386SX chip (for instance, on a bridgeboard) then these are the chips to go for!

Hope that helps some other crazy people like me for whom a clip-on chip just isn't good enough (or in my case, because the clip got old and became unreliable!)

--
Ian Gledhill
http://www.mutant-caterpillar.co.uk/shop/ for all your 8-bit and 16-bit needs!

Reply 1 of 63, by Anonymous Coward

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More or less good, but with a few minor problems

IBM 386SLC has 8kb cache, but the IBM 486SLC, SLC2 and SLC3 all have 16kb cache. You are correct they are 386SX bus compatible, but not pin compatible (as far as I've been told at least).

I don't know of any Tx486SLC2s. Do they exist? Can you show me a photo of one? The only one I know of from TI is the 486SXLC2, which is available as either 3.3V or 5V part. These are clock doubled, and have 8kb internal cache, both of which can be enabled or disabled at your pleasure.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 2 of 63, by Spirantho

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Thanks for the feedback!

Interesting points - I thought only the SLC3 had a different pin-out, but you may be right. It doesn't matter though - either way, the IBM parts are not valid replacements for a 386SX. As for the 486SLC2, there are a number of Chinese sellers apparently having them? Yet suspiciously no images anywhere. I'd guess the 486SLC2 is really a 486SxLC2, anyway - and, again, I suspect strongly is 3.3V not 5V (making it incompatible). You mentioned there may be 5V versions, which may work - do you have a part number for a confirmed 5V part?

--
Ian Gledhill
http://www.mutant-caterpillar.co.uk/shop/ for all your 8-bit and 16-bit needs!

Reply 3 of 63, by Anonymous Coward

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I am quite certain there are 5V versions, because I own two of them, and I remember checking them in the datasheet to confirm. I bought them as direct replacements for 386sx chips some time ago but never got around to soldering them in.

SXLC2.JPG

The other one is a 486SXLC 40MHz version (not clock doubled). I don't have a photo on hand though. It's also 5V.

Last time I checked chinese sellers had a lot of these...some of which were the 3.3v parts. I've only seen 50MHz parts available as 5V. All the 66MHz parts I've seen are 3.3V.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 4 of 63, by Old Thrashbarg

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Cx486SLC2-50MP = good! 50MHz power! This is the fastest I've found yet.

That's the one I installed on a Biostar 386SX-25 board here recently. It's a later board that has native BIOS support for the internal cache... older boards will require a software utility to enable it. It does indeed make a very big difference in performance, and it's a direct 'drop-in' swap (assuming you're good at SMD soldering, anyway).

Reply 5 of 63, by Anonymous Coward

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SMD soldering is a piece of cake. Just make sure you're using a low power iron.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 6 of 63, by Spirantho

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That SXLC2/50 looks interesting... I wonder what you can find them on...?
I have a TI 486SLC/25 which I tried on my A2386SX but it didn't work. I don't know if the chip is good, though.

For changing SMT chips I find an SMT rework station is by far the easiest. 😀 The low-end Aoyue beasties are great - not expensive but do the job brilliantly for simple SMT stuff. Certainly a lot safer than a soldering iron, though if you have to use an iron definitely a low heat controlled one is the way to go!

--
Ian Gledhill
http://www.mutant-caterpillar.co.uk/shop/ for all your 8-bit and 16-bit needs!

Reply 7 of 63, by Anonymous Coward

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http://www.ebay.com/itm/RARE-486-50MHz-TI-NEW … =item2a0f336ae6

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 8 of 63, by Spirantho

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That looks like it may be ideal!

However, I can't find a datasheet anywhere - does anyone know if it's 5V or 3.3V? I guess if there's no specs available the only way to be sure is to try it!

--
Ian Gledhill
http://www.mutant-caterpillar.co.uk/shop/ for all your 8-bit and 16-bit needs!

Reply 9 of 63, by Anonymous Coward

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I used to have this information, because at one time I needed to track down the information on programming the CPU init registers which are slightly different than the cyrix chips. As far as I know if the part is 3.3V it will be printed into the top of the chip.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 10 of 63, by Anonymous Coward

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2.31.7 Texas Instruments TI486SXLC-PAF CPU (Potomac)

Intel i80486 CPU instruction compatible, no FPU (Floating Point Unit).
Intel i80386SX CPU bus interface.

8 kbyte cache: write-through, 2-way set-associative, 1024 sets,
4 bytes per line.

33 MHz: february 1994.

Package: QFP (Quad Flat Package).

Technology: CMOS.

ID: step level A: DH = 0x04 (family ID), DL = 0x10 (model ID, revision),
step level B: DH = 0x04 (family ID), DL = 0x11 (model ID, revision).

DIR0 register: 0xFE.

2.31.8 Texas Instruments TI486SXLC-V-PAF CPU (Potomac)

Low power (3.3 V) version of the Texas Instruments TI486SXLC-PAF CPU.

25 MHz: february 1994.
33 MHz: february 1994.

Technology: CMOS.

ID: step level A: DH = 0x04 (family ID), DL = 0x10 (model ID, revision),
step level B: DH = 0x04 (family ID), DL = 0x11 (model ID, revision).

DIR0 register: 0xFE.

2.31.9 Texas Instruments TI486SXLC2-PAF CPU (Potomac)

Clock doubled version of the Texas Instruments TI486SXLC-PAF CPU.

20/40 MHz: february 1994.
25/50 MHz: february 1994.

Technology: CMOS.

ID: step level A: DH = 0x04 (family ID), DL = 0x10 (model ID, revision),
step level B: DH = 0x04 (family ID), DL = 0x11 (model ID, revision).

DIR0 register: 0xFE.

2.31.10 Texas Instruments TI486SXLC2-V-PAF CPU (Potomac)

Clock doubled, low power (3.3 V) version of the
Texas Instruments TI486SXLC-PAF CPU.

20/40 MHz: february 1994.

Technology: CMOS.

ID: step level A: DH = 0x04 (family ID), DL = 0x10 (model ID, revision),
step level B: DH = 0x04 (family ID), DL = 0x11 (model ID, revision).

DIR0 register: 0xFE.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 11 of 63, by Spirantho

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Thanks for that info!

I've tried several CPUs on my A2386SX: an AMD AM386SX/SXL-25, an i386SX, a Cyrix Cx486SLC/e-33-MP, a Cyrix 486SLC2/e-50 of some kind and a TI Tx486SLC/E-33PAF.
The only CPU that didn't work was the TI.
Is that a dead chip, or are the TI chips not drop-in 386SX replacements like the Cyrix modules?

Every 386SX upgrade that I've seen that uses a TI chip also has a logic board. The Cyrix 486 chip literally just clips on top of the 386SX - no other ICs at all - but the TIs all use extra ICs. I'm thinking therefore that only the Cyrix will work as a replacement CPU.

Has anyone ever actually managed to use a 486SxLC from TI to replace a 386SX chip?

--
Ian Gledhill
http://www.mutant-caterpillar.co.uk/shop/ for all your 8-bit and 16-bit needs!

Reply 12 of 63, by Anonymous Coward

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I've used TI486SXL as a direct replacement for 386DX in several boards. Some work okay and others don't. I suppose it's a bit more of a pain in the ass if you solder in an SXLC chip to your 386SX board and it doesn't work. At the very least all of my boards booted up just fine, some just didn't like certain features turned on. It was years ago and I don't remember specifics.

The Tx486SLC shouldn't have worked any differently than a Cx486SLC. It is an exact copy. Cyrix used TI's fabs to make the chip. The only difference between the two should be the label. TI 486SXL(c) chips are basically the same as the 486DLC except that they have a larger cache and remap one of the registers to turn clock doubling on or off.

I would guess that the reason you see chips on circuit boards is that they are 3.3V parts and need a voltage regulator to work in a regular 386 socket.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 13 of 63, by Spirantho

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One thing I've noticed about the Tx486SXLC upgrade chips is that not only are they on circuit boards, but they're all marked the same. They don't have a "V" marking for 3.3V, nor do they have "3.3V" written on them anywhere.
I think I'm going to stick to Cyrix - at least until I see word from anyone who's managed to put a TI chip in place of a 386SX, or I see a TI upgrade chip which doesn't involve an extra circuit board. A shame, really - those TI chips in the eBay auction are $5 or whatever instead of $45 for a Cyrix!
It just seems like there's loads of remaindered 3.3V chips around and very few 5V ones.

--
Ian Gledhill
http://www.mutant-caterpillar.co.uk/shop/ for all your 8-bit and 16-bit needs!

Reply 14 of 63, by Anonymous Coward

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Can you show me a picture of one of these upgrade chips?

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 15 of 63, by Spirantho

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There's one here:
http://www.cpucollection.ca/TI486SXLC2-G50-WN.jpg
It's clearly on a little board of its own so I think it must be an upgrade.
I did have a 50MHz upgrade I think at one point (ages ago) and it looked like this. I think it was a Make-It 486 board.

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Ian Gledhill
http://www.mutant-caterpillar.co.uk/shop/ for all your 8-bit and 16-bit needs!

Reply 16 of 63, by Anonymous Coward

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There are two chips on the adapter. One is a triple input NOR gate. Have no idea what that would be for. The other appears to be a VRM, which is strange since the chip doesn't appear to be a 3.3V model.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 17 of 63, by Cloudschatze

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Spirantho wrote:

There's one here:
http://www.cpucollection.ca/TI486SXLC2-G50-WN.jpg

I think it was a Make-It 486 board.

That's an Evergreen Tech., "REV TO 486" upgrade.

http://web.archive.org/web/19961104092136/htt … om/2sxinfo.html

I have one of these installed in a Tandy 1000 RSX. Works well enough, as long as a heatsink is attached.

Reply 18 of 63, by Jolaes76

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What is the name of the utility which enables L1 cache on 386 motherboards that do not have this option in their BIOS ? I suppose it should work with a 486DLC system as well.

"Ita in vita ut in lusu alae pessima iactura arte corrigenda est."

Reply 19 of 63, by Anonymous Coward

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I think it might be M5.EXE.

For the most part the DLC and SXL utilities are interchangable...except that you won't be able to turn on clock doubling if you use a DLC utility on a SXL.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium