MTRsystem1 (143K)

This page contains the details of a project being undertaken by David Fry and me to build a modern version of the Microtan 65 system. Many of the items developed are available for purchase at the shop here. A suitable starter project is described here.

The PCBs are being developed using KiCad (kicad-pcb.org). The KiCad project files have been archived in the ZIP files in the relevant sections below and include the Gerber files for PCB production.

EPROM Programmer
System Rack
Power Supply
Serial Keyboard Interface
TANBUS Extender


MT65-R (228K)

This is a modern replacement for Tangerine's latest version CPU card. It is fully compatible with the original and has the following enhancements:

  • UHF Modulator ASTEC UM1111 replaced with UM1233
  • Original character generator PROMs replaced with EPROM
  • Composite Video available via Phono connector
  • Option to wire in/out the 75R VDU shunt
  • Wire links replaced with jumpers
  • Option to utilise 2732 Monitor EPROM. Either of 2 images are user selectable by jumper

  • Schematic
    v1.0b KiCad archive (zip file)

    Bare MT65-R CPU v1.0b PCBs are available for sale in the Shop

    Character Generation EPROM

    The character generator map is burned into a 4k (2732) EPROM with either the upper 2k being the inverse (Rev1).
    Rev 1 code Binary Image
    or with the upper 2k being identical to the lower 2k (Rev2).
    Rev 2 code Binary Image

    Note: The FORTH programs require Rev2 code for its 'Words' to be displayed correctly. This is because the 6502 code stores Words with the 8th bit of the last character set to denote the end of the word.


    TANBUG v2.3 is Tangerine's updated monitor program compatible with the Microtan 65 (MT001 iss 1).
    Manual Appendix


    TANBUG v3.1 is Tangerine's updated monitor program that includes Tandos commands.


    TUGBUG is TUG's version of TANBUGv3.1.

    Note: TUGBUG cannot be used with a MT65-R CPU board in Single Board configuration (ie with the 3 links closed and no TANEX). Explanation here


    Tanex-Plus_10a (226K) <

    This is a modern replacement for Tangerine's Tanex card. It is fully compatible with the original and has the following specification:

  • A single AS6C1008 (128kx8) SRAM chip providing 64K memory ($400-$EFFF addressable).
  • 2 x 27512 EPROMs providing 8 pages of 12K EPROM to overlay $C000-$EFFF RAM memory space.
  • A single (user-selectable) IO memory location provided for selecting EPROM Memory Page to overlay $C000-$EFFF memory space or to leave this space as RAM. Default is EPROM Memory Page 0. LED indication of selected memory bank.
  • 2 x 16V8 GAL chips used for SRAM addressing and EPROM port addressing/bank selection.
  • 2 x 6522 VIAs unchanged providing 4 parallel ports. Four 8 x 2 IDC Header connectors to be used.
  • UART 6551 unchanged providing TTL level RS232 serial IO. Full 'true' RS232 level serial IO also provided by MAX238 chip - selection by jumper. IDC Header connector to be used. (Note: 20mA Loop circuitry is not retained)
  • Cassette Tape interface using 2 x LM358 but using Oric Tape interface design. 5 way 180 deg DIN socket connector (same as on Micron Front Panel).
  • Data buffering using 2 x 74LS244 chips.
  • Accepts TANBUS DMAREQ signal and drives TANBUS DMAGNT and ABE signal lines. Generates TANBUS ROME, RAME and IOE signals.
  • Note: UART 6551 may be substituted with 65C51 in PCB versions 1.0b and above.

    GAL Description Document
    v1.0b KiCad archive (zip file)

    Bare Tanex-Plus v1.0b PCBs and programmed memory are available for sale in the Shop

    X Bug EPROM

    Image F000-F7FF (G2)

    U13 EPROM

    U13 is the 27512 Eprom that holds the first 4 pages of memory that each map into the $C000-$EFFF area of the Microtan System memory. The following applications are provided:
  • Page 0 : BASIC + BASIC Toolkit
  • Further information
  • Page 1 : WORD Text Editor
  • (Code is relocated to $400-$13FF and is initiated with GC000 command). Further information
  • Page 2 : Microtanic's FIG-FORTH
  • Further information
  • Page 3 : Tansoft's 2 Pass Assembler v1.2
  • Further information

    Memory Map
    Binary Image

    GAL Files

    U3 PDS (text) file
    U3 JED (binary) file
    U7 PDS (text) file
    U7 PDS (binary) file

    64K RAM

    64RAM-RF (292K)

    A modern 64K RAM board produced by Barry Graham and is based on the TUG 64K RAM board. Note: This board is for use with the original TANEX. It cannot be used alongside the TANEX-PLUS as both board address the same memory range.

    Full details are available on Barry's web-page.



    TANDOS (177K)

    Modern replacement for the Tangerine TANDOS 65 board.

    - Appendix A - TANDOS Commands
    - Appendix B - HxC Option
    - Appendix C - Using 3.5" Disk Drives
    Photo showing HxC fitted
    v1.0 KiCad archive (zip file)

    EPROM U17

    EPROM U17 is a 2732 EPROM containing both the TANDOS and DBASIC images.

    TANDOS Listing
    DBASIC Listing
    Image (Intel format)
    Image (Binary)


    HRG-R (199K)

    This is a modern replacement for the Tangerine High Resolution Graphics (HRG) board.

    Provides 256x256 pixel high resolution graphics screen. When used with the HRG Toolkit can also provides a 51 character x 45 line high-resolution text screen. Modulated UHF and composite video outputs available.

    Schematic v1.0b
    HBASIC A TANDOS utility for loading / initialising 'Disk' BASIC and the HRG Toolkit (for use with the TANEX-Plus)
    v1.0b KiCad archive (zip file)

    Bare HRG v1.0b PCBs and programmed Toolkit EPROMs are available for sale in the Shop


    SoundBoard-R (286K)

    This is modern replacement for the Bulldog Soundcard. It includes a battery backed Real Time Clock module. The PCB design, Manual and supporting software were developed by James Price. It has the following specification:

  • A double sided PCB suitable for use with a Microtan-R backplane.
  • 3 voice sound as default and a further 3 voices available as an option.
  • Audio waveforms provided by the AY-3-8910 sound chip.
  • Onboard 300mW LM386 based audio amplifier and integral speaker including volume control.
  • Optional components to increase amplifier gain if desired.
  • Line level output.
  • Optional battery backed highly accurate (5ppm) Real Time Clock (RTC).
  • Optional 32Kbit EEPROM memory.
  • 16 (32) general purpose I/O ports.
  • Optional system Power On Reset function.
  • Header pins for I2C and RTC expansion / monitoring.
  • Audio, RTC and EEPROM memory functions are programmable / controllable from BASIC and machine code.
  • The addresses occupied by the sound card within the Microtan memory map are configurable.

  • Manual

    Supporting Software

    SNDEMO.txt - Sound demo program in BASIC
    RTCBAS.txt - RTC demo program in BASIC2
    RTCHYB.txt - RTC demo program Machine code core + BASIC wrapper
    EEPBAS.txt - BASIC Test program for the EEPROM chip on the RTC module
    MC2DAT.txt - BASIC program for converting bytes in memory to BASIC DATA statements
    i2c_asm_mt.asm - Assembly source file for the RTC machine code routines
    i2c_lst_mt.lst - Assembled listing for RTC machine code routines

    Because of the size of the associated .wav files, they are held on my FTP server. If you wish to download any of these files, please send me an email (address is on the Home page) and I will provide access information. All .wav files have been saved at 'FAST' speed.

    James has also been experimenting using the soundcard as a musical instrument. He has generated a document that captures the various steps he has taken.
    The associated software files are also available on my FTP server.

    MT-R EPROM Programmer

    MTREP (216K)

    This EPROM Programmer is capable of reading and programming 2716 and 2732 EPROMS. It connects to TANEX parallel port sockets A,C and D and requires an external power supply to provide the Vpp programming voltage.


    Software for the MT-R EPROM Programmer board resides in memory at $400-$7C1.
    Program Listing


    KB_R (262K)

    Replacement for Tangerine Keyboard (MT020)

    The circuit is identical to MT020 Issue 3 except the mechanical Caps-Lock switch is replaced by a software toggle function.

    KiCad Archive (zip file)

    Photo of Keyboard in its case.


    Keypad2 (44K)

    Replacement for Tangerine Keypad

    KiCad Archive (zip file)

    System Rack

    What started life as a bespoke 19 inch 4U system rack has been modified to accommodate the Microtan Circuit Boards and fit into my existing Vero 19 inch enclosure. This involved removing the end plates, cutting them down to size and re-drilling the holes for the screws that hold the 6 longitudinal rails in place.


    MB_MT-R1 (244K)

    The motherboard has been designed to accommodate CPU, TANEX and 5 expansion slots. The slots are 1 inch apart to allow for a wider PCB form factor and increased cooling. Tanbus expansion slot signal lines 19b and 20b have been earmarked for Video1 and Video2 signal. Each may be configured by on-board jumpers to link to Tanbus CPU slot signal lines 19a or 20a.

    This motherboard has now been replaced with a prototype for the full-sized Backplane-R described below.

    KiCad Archive (zip file)
    Photo (rear)
    TANBUS Connections
    TANBUS Signal Descriptions

    Full-size Backplane

    Backplane_RF (312K)

    The Backplane-R is a direct replacement for the Tangerine MT0010 Backplane. It accommodates CPU, TANEX and 9 expansion slots. Again the slots are 1 inch apart and expansion slot signal lines 19a and 20b earmarked for Video1 and Video2 signals as described above.

    The onboard circuitry provides buffering for the O1, O2, CLK, SYNC signals from the CPU. Additionally Memory Page management for the memory range $2000-$BBFF is possible utilising the Block Enable signal. A full description is available here. However, this can only be used when an original TANEX is fitted. If a TANEX-PLUS is fitted with its $2000-$BBFF memory permanantly enabled, then this range cannot be overlaid by other boards.

    Photo (rear)
    TANBUS Connections
    TANBUS Signal Descriptions

    Power Supply

    PSU (215K)

    Power is supplied to the motherboard by a 65W Meanwell 1496-RQ-65B Quad Output enclosed power supply providing dual 12 volt and 5 volt supplies.

    Other Projects

    Serial Keyboard Interface

    PS2adapter (88K)

    Construction notes for creating a Serial Keyboard interface to the Microtan 65 supplied by Danny Page. This interface enables a PC-AT keyboard to used with the Microtan system.

    Circuit Diagram
    PIC16F84 Assembly code
    PIC16F84 Intel-HEX code
    Project Notes
    KiCad Archive (zip file)

    TANBUS Extender

    Extender (182K)

    Plugs into any TANBUS slot on the motherboard. Microtan board under test plugged into the extended socket. Allows work to be undertaken on a Microtan board under test outside the system rack. Test points available for all TANBUS signal lines.

    Other Data

    Memory Map

    MemoryMap (63K)

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