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386EX marking question: EXTB or EXTC... (3.3V or 5V)? [message #7988] Wed, 30 September 2020 06:30 Go to next message
just4fun is currently offline  just4fun
Messages: 273
Registered: May 2017
Location: Dark side of the Moon
Senior Member
Hi, I have some 386EX25.

Accordingly with the datasheet (see attachment) there are at least two variants: EXTB running at 3.3V and EXTC at 5V.

In the marking I see a TB in the third row (see photo)... so I guess that they are EXTB so running at 3.3V (and the EXTC parts seem to be rated @ 33MHZ).

/forum/index.php?t=getfile&id=1881&private=0

Anyone with any experience with this marking can confirm that the marking in the photo is for EXTB so 3.3V parts?
Re: 386EX marking question: EXTB or EXTC... (3.3V or 5V)? [message #7989 is a reply to message #7988] Wed, 30 September 2020 14:08 Go to previous message
Yves-D. is currently offline  Yves-D.
Messages: 21
Registered: January 2020
Junior Member
I googled a bit around on the EXTB/EXTC thing, while clearly explained in the datasheets - there's absolutely no info on the case markings and where to find them. Mystery stuff...
Other manufacturers often feature an illustration of the CPU package and the position where the markings are to be found.

Initially I thought that EXTB/EXTC might only be a CPU-binning designation: if the CPU passes the 3.3V test it is being marked EXTB, but that's not the case.
The 3.3V and 5V processors seem to be distinct parts.

I checked on x86.fr. This chap has quite an extended X86 CPU collection and even built his own CPU tester (the UCA - quite a feat!Wink
Unfortunately he doesn't talk about the 386EX

John Coffman did a 386EX 5V design over here: https://www.retrobrewcomputers.org/doku.php?id=boards:sbc:sb c-386ex:rev2.0
All pictures show the TC marking.
I'm quite sure that yours is the 3.3V part
Perhaps John can shed some insight on the issue when you ask him.

Yves

[Updated on: Wed, 30 September 2020 14:17]

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