Search Posts:

MS-DOS S-100 Bus Board


Return to Threads

  MS-DOS S-100 Bus Board by John Monahan - 03/31/2012 22:21
For those that may be interested I have written up a detailed description and construction details of the new MSDOS Support S-100 bus Board that Andrew & I have completed. A while back we decided to try and put together a kind of "catch all" S-100 board that would cleanup some loose ends need to easily run MSDOS on an S-100 system and with our future CPU boards. Here is what we could fit on one S-100 board.

Please go here for more information:-

In Summary the board contains:-

8259A PIC
First of course we need an 8259A interrupt controller. The chip is hard wired to ports 20H and 21H -- ports almost ever PC 8259A in the world is hard wired to these ports!

One very useful feature we found on one of our earlier PIC-RTC board was the LED bar that stretched any one of the eight S-100 bus interrupt pulses out to a visible light flash. I added this useful debugging feature to our MS-DOS board.

This is the most important component on the board. This chip is 100% software compatible with the PC-AT CMOS RTC chip and one can access the chips onboard RAM. On all PCs the RTC is on IO ports 70H and 71H. This is hard wired as such into our board.

8254 Timer
All PC's use this timer. It is kind of underutilized though. Of the 3 timers on the chip, one is used for the system tick. Another is used to generate sound on a small speaker. The speaker is driven by a 75477 chip. The PC uses an unusual clock frequency (1.193MHz) to drive the timer. We generated this frequency using a common 14.318 MHz TV oscillator and a 74LS92 divide by 12 counter. The counters can be configured to trigger any one or the S-100 bus interrupt lines (as on the PC).

EEPROM Circuit
For 8086 boards that do not have (or have a limited) an onboard boot ROM capability, we added two sockets and support circuitry to support 28C64 and 28C256 EEPROMS. The EEPROMs can be located anywhere in the S-100 address space so they could be used for video or network card drivers.

Two Wait State Circuits
The board has a wait state circuit for the above dual 16 bit wide EEPROMS. From 0 -8 wait stares can be added for any CPU access.

However the board has a second wait state circuit that is a bit more unusual. This circuit allows you to insert 1-8 wait state "holes" anywhere in the S-100's address space to accommodate a pocket of slow access RAM


  8088 S-100 board update by Bill Degnan - 04/10/2012 21:10

For those interested in S-100 Bus systems, Andrew Lynch & I (John Monahan) have just finished constructing a new 8088 S-100 bus CPU prototype board. For those interesting in moving from 8 to 16 bit systems on that bus this is an easy stepping stone rather than going directly into a 16 bit CPU board. The hardware is a little simpler in handling the 8 rather than 16 bit data lines. We currently have a Z80, 6502, 8086 and 68000 CPU set of S-100 boards. Under construction are 80286, 80386 and 80486 boards as well a number of other CPU, video boards etc.

Please see here for more information:-



Buy a Commodore Computer Poster

Popular Topics and FAQs

  • Commodore B Series Tips and Tricks
  • Aerocomp TRS 80 M 1 Expansion Unit DDC
  • Items Wanted
  • Lobo Max 80
  • Zenith Z-19-CN
  • Prototype PET 2001 photo
  • Using Toggle Switches to Analyze Memory
  • Commodore Disk Archive Project
  • PET 2001 Prototype at Gametronics 1977
  • Jim Butterfield Photo
  • IMSAI 8080 With Processor Tech. Cutter
  • Secrecy is the keystone of all tyranny
  • Cromemco System Three
  • Northstar Horizon - Boot Problem
  • Computer History and Restoration Links
  • Commodore BX-256-80 - 8088 Co-processor
  • S-100 board testing with Z-80 ICE
  • Donner 3500 - an early portable computer
  • Digital (DEC) PDP 11/05 NC Assembly
  • Univac 1219 rescue
  • Fido BBS listing node list 6-13-1986
  • PDP 8e
  • MITS 88-2 SIO (2SIO) for BASIC
  • Visual Technology Inc Model 1050
  • Amiga 2500 Restoration
  • The Evolution Of IBM Computers
  • Replacement teletype print hammer head
  • Archiving and Copying Software 101
  • Computers Built 1940 - 1950
  • CBM B-520 (a.k.a B256-80 or B500 256)
  • RCA COSMAC Microkit
  • Commodore 64K C-116 Mods
  • MITS 8800b Turnmon 9600 baud
  • Catweasel, 8in and 5 1/4
  • Raspberry Pi as Gateway to Internet
  • Digital PDP11 late 1969 early 1970
  • PDP 11/40 72 inch cabinet model
  • PDP 11/40 Industrial 11 model
  • Digitial MicroVAX 3100 30 System
  • Digital VAX 4000-200
  • Commodore 64 / 1541 DRIVEKNOCK
  • Booting the System Using RL02 drive
  • PACS: Reflections by Kathleen Mauchly
  • Tele-Graphic Computer Systems Inc.
  • Commodore B Series SID Jukebox?
  • Installing Core into PDP 11/40
  • Setting Up OpenVMS 7.1 DNS CLERK
  • Felt-Tarrant Comptometer Model J
  • NextStation Color
  • Digital Rainbow (PC100-B2)
  • 1970 Compusad Compulogical Tutor
  • Archiving Papertapes Using DSI NC 2400
  • 1976 P.C.C. Features the MAI JOLT 6502
  • 1961 Beckman DEXTIR Computer
  • UNIVAC 1 and UNIVAC File Computer 1
  • Past Issues:

    tcf 2008 digital pdp8 sn1158 front panel d

    This image was selected at random from the archive. Click image for more photos and files from this set.