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• The magazine article

  Keith • 03/10/2023 at 20:02 • 0 comments

  Micro Cornucopia number 32, (October/November 1986)

  Public Domain 32000

  By Dave Rand and George Scolaro

  72 Longfellow St. Thousand Oaks CA 91360 (805) 493-1987

  World’s Cheapest Unix System

  Contents

  • Public Domain 32000: The Hardware
    How to put together a UNIX co-processor system
    (complete with UNIX V) for under $1,000.
  • Public Domain 32000: The Software
    The software end of this UNIX compatible.
  • PALs — What They Are And When To Use Them
    Why the 32000 UNIX system was designed with PALs

  The Hardware

  This is for all of you who want to put a computer in your clone or CP/M machine. (Sorry, that was a cheap shot.) Actually, this is the cheapest way known to hacker or human to build a truly powerful system (UNIX System V if you wish).

  With hardware floating point that outruns DEC 11-70s, 2 Meg of DRAM, DMA, and a memory management chip, this $400 system is an incredible hardware bargain. See the SOG V article in this issue for information on a public domain operating system for this machine.

  Our primary goal in designing 32000 based system was to come up with a low cost system without compromising performance. One of the unique aspects of the design (which was first presented at SOG V) is that it has been released to the public; schematics, PAL equations, interface software, and the PCB artwork. For this reason, we named our design PD32. (We are, however, restricting commercial copying of the system, see the note at the end.)

  We chose the National Semiconductor 32000 chip set (second-sourced by Texas Instruments) because it’s inexpensive, is a mature product, and was designed to support high level languages. The total cost of both the hardware and UNIX System V, with which the system runs, should be under $1000.

  The version of UNIX available for this board is the full AT&T UNIX System V release 2. The port was performed by ZAIAZ Communications and is AT&T and National Semiconductor approved.

  About The 32000

  The 32000 series includes the timing control unit (TCU), the central processing unit (CPU), the memory management unit (MMU), the floating point unit (FPU), and the interrupt control unit (ICU). Currently four CPUs are available in the 32000 series; they are the 32008, 32016, 32032, and 32332.

  The 32000 series is unique in the microprocessor world in that it is the only family that maintains 100 percent upward and downward software compatibility at the binary level. This compatiblity means the end user doesn’t need to change software when changing CPUs.

  Of the four CPUs, we chose the 32016 for its price and ease of board routing (the board has only two layers). The 32016 still has a full 32-bit internal architecture but has a 16-bit external data path. To reduce pin count both the CPU and MMU multiplex their data and address buses. In other words, data and address information are put on the same set of pins.

  Hardware Design

  Now that we’ve covered some of the background, let’s take a close look at the design. From Figure 1 we can see that the TCU, CPU, MMU, and FPU figuratively bolt together. To understand how the rest of the system interfaces to these four devices, we need to understand the timing of a bus cycle.

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  Figure 1. Main Processor Section

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  Addressing

  The CPU places the logical address onto the data/address bus during T1 and pulses its address strobe (ADS) pin. If an MMU is in the system (as in this design) ADS from the CPU connects to ADS of the MMU. The MMU then performs any necessary page table lookups and translations, places the physical address onto the data/address bus, and pulses the physical address valid (PAV) pin. This is performed in the TMMU state.

  This pin becomes the system-wide address strobe pin and also connects into the TCU. The TCU, on receiving the ADS signal, generates either a read (RD) or write (WR) signal during T2 and T3. During T2 and T3 the bus becomes a data bus with data either being read or written by the CPU or MMU. The final T4 state is used internally...

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