ARB-11: A Homebrew PDP-11 Computer

      This web site is being brought to you from a homebrew
   computer designed to emulate a PDP-11/34. The core of the
   computer took about two years of spare time to design and
   build. The machine has a 32-bit wide microcoded instruction
   decoder and a 96-bit wide microcoded sequencer with a basic
   microcycle time of 250 nanoseconds. The 32-bit CPU uses 8
   AMD-2901C 4-bit slice arithmetic/logic units wired to
   perform 8, 16, 24, and 32-bit operations. The machine has
   4K words of instruction decoder and sequencer microcode.
   The machine was coded to emulate the venerable PDP-11/34
   instruction set and uses UNIBUS I/O. Additionally the
   FP-11 and FIS (PDP-11/35) floating point was also coded.
   The basic PDP-11 instruction set programmed in 256 words
   of decoder and sequencer microcode. The EIS, FIS, and FPU
   microcode required 768 additional sequencer words. This 
   code was programmed into bipolar proms as the machines native
   instruction set. The remaining 3K of decoder and sequencer
   microcode is high-speed programmable static ram which can
   be loaded on the fly with whatever extension instructions
   you might wish to implement (e.g. a block memory-to-memory
   move instruction). The machine executes most single operand
   register and double operand register-to-register
   instructions in .75 microseconds (3 microcycles). The
   machine is benchmarked at slightly faster than the
   PDP-11/34 (with a FPU).  This machine was my development
   platform for many microprocessor based projects and uses
   the RT-11/TSX-Plus operating systems.
      The core computer, which includes a keyboard, a hand pull
   paper tape reader, video controller, serial printer interface,
   and the power supplies, was constructed on 11 14x20 inch
   planes.  Each plane contains 4 7x10 inch single sided printed
   circuit boards.  Each circuit board only distributes power
   to wire-wrap sockets for the core processor components.  Most
   components are small and medium scale TTL devices abundantly
   available from 1976-1985. Pictures of the system and
   individual panels were taken in 2012.  Some video clips of
   the computer can also be viewed.

Current System Configuration

      The current system configuration, as of August 2012, includes
   the following items:

      1) Core processor with a microprocessor (6800) console
         with video output for a CCTV B/W monitor.
         The microprocessor includes built in boot code for
         the RX01 (DX), RX02 (DY), RK05 (RK), and TM11 (MT)
         devices and a general support program KUS (Keyboard
         Utility System) which features a non RT-11 file system
         used to save/load image files for diagnostics.
         A console pass through serial port was initially used
         to connect to a LA120 DEC Writer as a printer but now
         is connected to a secondary console terminal.

      2) peripherals chassis with
         a) UNIBUS DD11 backplane
         b) ADAC Model 1900 UNIBUS to QBUS converter
         c) QBUS DDV11 backplane

      3) UNIBUS peripherals
         a) CRDS 411 Double-Sided / Double-Density
            8" Floppy Disk System
         b) TD Systems Incorporated Viking Series
            SCSI Host Adapter UDT Disk/Tape Controller
            with a Seagate disk drive and
            Transitional Technology, Inc. (TTI)
            Series 2200 Cartridge Tape System
         c) Western Peripherals 131 TM-11 Tape Controller
            with Cipher Data Products 100x 9-track
            45 ips 800/1600 BPI tape drive
         d) DELUA network interface card
         e) MDB-11C general parallel interface card
         f) Homebrew EPROM and Bipolar PROM programmer

      4) QBUS peripherals
         a) Heath Kit H-11-5 Serial Port Cards (6)
         b) an ADAC 1953BR QBUS repeater interface
            connected to a Data Display system
         c) a Decmation D201/D100 Z80/8088 Co-Processor
            running CP/M and MSDOS 2.1 from virtual

      5) Heath Kit H19 terminal with the SUPER-19
         replacement ROMs emulating an enhanced
         VT100 terminal.

      6) SB180 microcomputer with four 5 1/4" floppy disks
         connected via serial ports (console and modem).
         ZCPR3 is the installed operating system.

Comparative Execution Speeds

      Some relative execution speeds for compiling the TCP/IP
   Package for RT-11/TSX-Plus on the homebrew-11, LSI-11/73,
   PDP-11/44, and John Wilson's Ersatz-11 PDP-11 emulator
   are interesting:

      Homebrew-11        5261 seconds    x0.64    ( 7 Apr 2012)
      PDP-11/44          3920 seconds    x0.86    (25 May 2012)
      LSI-11/73          3370 seconds    x1       (11 Apr 2012)

      (AMD Phenom II @3.6GHz):
      Ersatz-11 V2.1       49 seconds    x68      (15 Sep 2012)
      Ersatz-11 V6.0       18 seconds    x187     (15 Sep 2012)

Last Updated: August 2012