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Heath/Zenith- H/Z-110 Motherboard
While a few other S-100 computer companies had some support logic on their motherboards, for example Vector Graphic, only Heathkit had the CPU, support RAM/ROM and I/O (including video) on the motherboard.   In fact the S-100 bus in the H/Z-100 system was used only for specilized components like a FDC or hard disk controller.

Heathkit H/K-100 Motherboard

While clearly not an S-100 board I am including this motherboard here because it accommodated S-100 boards and had much of the functionality of a S-100 SBC board itself.

The Z100 was a dual CPU machine featuring both an 8085 and an 8088 CPU. There were actually two machines produced. A Z-110 which did not contain a CRT display and a Z-120 which had a completely integrated CRT display with its own separate video board. The motherboard for both units was the same.

The machine featured very advanced (for the day) bit mapped video that allowed up to 640 x 512 pixels of 8 color graphics to be displayed.  The board contained both an 8085 and 8088 CPU for maximum software capability. The units also had switching power supplies rather than bulky transformers so common at the time.

An excellent "all in one" schematic can be obtained here.  A few interesting points. The S-100 status signals are put together via a 74S288 bipolar PROM chip. The system clock (5Mhz or 8MHz) was generated with a 8284A. A lot or high speed ALS 7400 type chips were utilized. There were two  onboard 8258 programmable interrupt controllers. The pin 49 2MHz signal was generated directly with its own 4MHz oscillator.  MWRT was generated in the standard manner on board. There was detailed circuitry to glitch free handle CPU master swap control.  All in all the layout was very nicely done and would be familiar to any S-100 expert.  There a number of variations of the above basic motherboard with increasing RAM and clock speeds.
 Model 85-2653-1      192K RAM  (3X 64K Dynamic RAM)  5Mz Clock
 Model 85-2806-2      768K RAM  (3X 265K Dynamic RAM)  8MHz Clock

A more detailed schematic can be obtained here.  The beautiful manual for this computer can be obtained here.
(The manual is actually in two parts. Part 2 is just for the video board). These manuals are large.


Heathkit S-100 Boards
Motherboard    FDC      Winchester Disk Controller   256K RAM    ARCNET


This page was last modified on 10/25/2013