SBC-188 version 3


The SBC-188 version 3 is an update and improvement to the earlier board. This board is better suited for 80C188 operation at 25Mhz.

  • Memory size is increased to 1Mb, allowing a full DOS memory of 640K plus high memory blocks.
  • The 82C55 controller is configured as a PPIDE (parallel port IDE) connection; it works with hard disks as well as CF cards.
  • An IDE8 connector directly on the CPU data bus is added.
  • The floppy controller and connector are present. Drives may be 360K, 1.2M, 720K, or 1.44M.
  • Status LEDs indicate the sequence of boot-time P.O.S.T. diagnostics.
  • The Serial I/O UART connector is altered to support RTS/CTS protocol, or crossed to DTR/DSR protocol.
  • The board may be used stand-alone by powering it from the IBM 4-pin peripheral connector. In this case a terminal or terminal-emulator is attached to the serial connector.
  • The board may also be inserted into any RetroBrew ECB backplane to connect to peripheral boards, including the 4MEM, DualSD, ColorVDU, VGA3, etc.
  • ROMs supported may be 32Kb, 64Kb, 128Kb, or 256Kb. The current BIOS recommended is 64Kb.
  • The board runs MSDOS 5.0 or MSDOS 6.22.

The Board

The bare board layout:


Finished board, ROM in raised ZIF socket for BIOS development & checkout:


File List

FilenameFilesizeLast modified
sbc-188v3.1-004-sch.pdf 491k22-Jan-2020
sbc-188v3.1-004-pcb.pdf 1151k08-Jan-2020
sbc-188v3-board-errata.txt 2k22-Jan-2020 3.2K02-Dec-2019
sbc-188v3.1-004-bom.csv 2k22-Jan-2020
sbc-188v3.1-004-bom.png 252k22-Jan-2020 1202k08-Jan-2020 433k07-Feb-2020
dma_on_sbc-188_v3.pdf 53k08-Feb-2020

BIOS software is here.

Version 3 of the SBC-188 is designed to support DMA access to main SRAM memory by controllers on boards on the ECB bus. Documentation for DMA access for anyone interested in creating an I/O board that uses DMA is available above. There is at this time no such ECB board; hence, the document may not be of general interest.

Board Details


The two types of Super Capacitors may be used for the RTC/NVRAM backup. Second photo shows 13.5 mm diameter cap; third photo shows a vertical mount. I used this 1.5F cap, and consider that value too large: I had to leave the board powered up overnight to get enough charge in the cap to bring the voltage above 2 volts. The good range would be 0.22F up to 0.47F. The cap in photo 2 is 0.33F.


Left photo shows the normal jumper setting for the RS-232 interface to allow RTS/CTS line protocol. The right photo shows an alternate setting which crosses RTS-CTS to DTR-DSR. This is for terminals that use the obsolete DTR/DSR line protocol. However, the programming within the UART is still RTS/CTS. If you have any doubt about which setting to use, use the one on the left.


The left photo shows a rather odd jumper (P601) labeled “INT2/INTA0”. It should always be set to “INT2” (1-2); the other setting (2-3) is for a possible future use. To the right is jumper (K601), the “Legacy/Kontron” Reset setting. In the Legacy setting (1-2) reset is put out on DIN pin C31; with the Kontron setting, DIN pin C31 is a Reset switch input to the CPU board, and the Reset signal is correctly put out on DIN pin C26 (RESOUT). All peripheral boards should also use the Kontron setting. (Kontron, a German firm, manufactured one of the earliest Zilog Z80 computers that used the 96-position DIN connector, and this was the intended pin usage.)

The right photo also shows the IBM peripheral connector, which may be used to power the board as a truly Single Board Computer, SBC-188.

Screen Images

This is a boot screen using a Wyse terminal for keyboard input and screen output:

This is the boot screen with the SBC-188 v.3 used with the VGA3 board. An IBM PC keyboard is the input device, and a VGA capable LCD monitor is used for output:

SBC-188 (original, v.2)


The SBC-188 is a Single Board Computer using the 80C188 CPU. General features include:

  • CPU 80C188-16 w/512K SRAM
  • UART 16c550
  • ParPort 8255
  • Floppy Controller WD37C65B
  • ECB RetroBrew bus for expansion

This is the layout of the rev. 2.0 board: (anyone have a photo? I still run the 1.0 board)

Build Information

Builder's Notes/Comments

Please use this space to add any notes/comments on this board that don't fit into the above sections. (Periodically, these comments may be re-arranged to be better incorporated into a new revision of the wiki page.) Please sign your comments using the wiki “Insert Signature” feature!

File List

FilenameFilesizeLast modified
dma_on_sbc-188_v3.pdf52.9 KiB2020/02/08 13:01
gal-3.0-002.zip3.3 KiB2020/02/01 11:35
img_1353.jpg749.5 KiB2020/01/25 12:37
img_1356_crop.jpg767.9 KiB2020/01/25 12:37
img_1360.jpg202.6 KiB2020/01/26 15:10
img_1364.jpg139.6 KiB2020/01/26 15:10
img_1367.jpg113.9 KiB2020/01/26 15:10
img_1375.jpg92.7 KiB2020/01/26 15:10
img_1376.jpg90.3 KiB2020/01/26 15:10
img_1377.jpg650.6 KiB2020/01/25 12:37
img_1379.jpg562.3 KiB2020/01/25 12:41
img_1380.jpg125.2 KiB2020/01/25 12:41
img_1381.jpg118.8 KiB2020/01/25 12:41
img_1382.jpg116.9 KiB2020/01/26 15:10
sbc-188-2-007mfg.zip156.8 KiB2017/04/11 10:19
sbc-188-2.0-component.png101.2 KiB2017/06/21 16:05
sbc-188-2.0-kicad.zip433.4 KiB2017/04/11 10:19
sbc-188-2.0-parts_list.txt5.9 KiB2017/04/11 10:19
sbc-188-2.0-schematic-007.png669.1 KiB2017/04/11 10:19
sbc-188v3-board-errata.txt1.9 KiB2020/01/25 12:49
sbc-188v3.1-004-bom.csv2.4 KiB2020/01/25 12:48
sbc-188v3.1-004-bom.png246.2 KiB2020/01/25 12:48
sbc-188v3.1-004-mfg.zip1.2 MiB2020/01/25 12:49
sbc-188v3.1-004-pcb.pdf1.1 MiB2020/01/25 12:49
sbc-188v3.1-004-sch.pdf491.1 KiB2020/01/25 12:48
sbc-188v3.1-004.kicad.zip4.2 MiB2020/02/07 11:37
sbc188-vga3-boot-lg.png589.7 KiB2020/01/25 10:40
sbc188-xterm-boot-lg.png516.7 KiB2020/01/25 10:40

boards/sbc/sbc-188/start.txt · Last modified: 2020/02/19 15:40 by jcoffman
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