SBC-386EX rev 2.0 Board

Disclaimer: as of the end of 2018, the BIOS ROM is still a work in progress.

N.B.: The 2.0 board requires a 1-wire update (see section below).


386EX User's Manual


  1. 80386EX CPU running at 25Mhz or 33Mhz
  2. FPU socket for 387SX
  3. Serial I/O using CPU integrated 8250A
  4. DS1302 RTC and NVRAM
  5. 32Kb SRAM
  6. 72-pin DRAM supports 4Mb .. 64Mb
  7. IDE interface
  8. micro SD socket
  9. ROM socket for 64Kb .. 256Kb BIOS chip
  10. All of the on chip features of the -EX chip



Photo 1. Dan's board using the CPU mounted on a daughterboard.

www.retrobrewcomputers.org_lib_plugins_ckgedit_fckeditor_userfiles_image_boards_sbc_sbc-386ex_jrc-386ex-img_0988.jpgPhoto 2. John's board with the CPU board-mounted.

www.retrobrewcomputers.org_lib_plugins_ckgedit_fckeditor_userfiles_image_boards_sbc_img_0941_sm.jpgPhoto 3. Two of the adapter boards for the 386EX.

Suggested technique for soldering the PQFP-132 386EX:

A. Coat the PQFP board pads with liquid flux. IMPORTANT.
B. (optional) Tin the board with a flat tip iron with MINIMUM solder. This is not necessary if the HASL layer has enough solder to attach the chip pins.
C. Coat the bottoms of the PQFP pins with liquid flux.
D. Position the PQFP; tack down corners with a DRY (solder-free) flat or wedge tip iron. Re-check positioning constantly.
E. Finish heating all of the pins with the DRY flat or wedge tip iron until all pins pass visual inspection under a jewelers loupe (8X) magnifier.
F. (optional) If you have a low voltage (<3v) tester, buzz out the connections with straight pins used as probes. This is tedious.

Hardware Documents

FilenameSizeLast modified
update-2018-02-18.txt 432b2018-Feb-18
sbc-386ex-2.0-sch.pdf 499kb2018-Jan-21
sbc-386ex-2.0-pcb.pdf 850kb2018-Jan-21 4kb2018-Feb-18 1.4mb2018-Jan-23 955kb2018-Jan-21

There is a Guide to the Schematic which may be of interest to some builders.

The current Kicad tools do not produce a very pretty Bill of Materials. This “CSV” (comma separated values) is edited to add additional information.

www.retrobrewcomputers.org_lib_plugins_ckgedit_fckeditor_userfiles_image_boards_sbc_sbc-386ex_jrc-386ex-2.0-to-2.1-update-img_1078.jpgBoard 2.0 to 2.1 (mandatory) update.

Adapter board

FilenameSizeLast modified
adapter386ex-sch.pdf 90Kb 2017-Nov-08
adapter386ex-kicad.tar.bz2 193Kb2017-Oct-09 73Kb2017-Oct-09

Note: This adapter is not for other PQFP-132 chips. Power and Ground connections are specific to the 80386EX chip.

Software Tools

The software for the SBC-386EX has been developed under Windows using:

  1. The Netwide assembler, NASM 2.08
  2. Open Watcom 1.9 (2.0 should not be used)

In addition, certain tools, largely derived from the SBC-188 project will also be required:

Board Testing

Proper operation of the DRAM should be confirmed with:

The ROM images are distributed as *.HEX files in the archive. (Intel Hex)

boards/sbc/sbc-386ex/rev2.0.txt · Last modified: 2019/02/11 05:29 by b1ackmai1er
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