Hitachi HD6303 Monitor

Micro6303 Cold Boot

It lives!

The Hitachi 6303 is a variation on the Motorola MC6800/6801/6803 Motorola microprocessors and microcontrollers from the late 70’s and early 80’s.  I have an interest in reverse engineering embedded systems from that era.  Previously I have created a 6809 EPROM Monitor program called Micro09 and later a variation call Micro11 for the Motorola 68HC11.  The latter is still available on the web in a few places.  This new one, Micro6303, is basically the same beast, except for the 6303.

Micro6303 Main Menu

Micro6303 Main Menu

In all cases the idea of a Monitor is to create a development OS of sorts that can run on a minimal hardware setup.   A serial port is used for communication with the embedded system and a timer is used for single-stepping code.  The HC11 and 6303 have the timer and Serial Communications Interface on the chip, so that simplifies the hardware required to bring a system “up”.  But still quite a few components are required compared to today’s flash microcontrollers.

Micro6303 CPU Window

Micro6303 CPU Window

Anyway, without further adieu, here are some screen shots of the Micro6303 EPROM Monitor including the Cold Boot screen, the Main Menu and the CPU Window which is the facility for single-stepping and setting breakpoints. It is a work in progress and I will release binaries in the near future.

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10 Responses to Hitachi HD6303 Monitor

  1. Awesome project! Keep me posted.
    I have some old HD6303X PCB’s. These supported both Ram/Rom up to 32K, and expansion header. I had documented source to a nice monitor from Hitachi, but went through some bad times and chucked most of my hobby soft/hardware disks, parts, books etc. I still have the image in eprom, it has a built in disassembler and you can save an SREC to PC. If interested, I could send/mail one PCB/Sch to you? It’s a project of mine to update this board, ie. USB and win32 IDE GUI interface.

    • grantb4 says:

      I would definitely be interested! USB? I think it’s easiest to just go the FTDI RS232-to-USB route. It’s very solid, not sure if that’s what you had in mind though. It’s hard to find a USB controller that you can hook up to an expanded addr/data bus.

      • Jules Marchildon says:

        Hello grantb4,
        Sorry I left you hanging! It’s been awhile, I’ve been off sick for a number of years. Now feel well enough to jump back into the saddle. I pulled out what’s left of my EMC-03 kit. PCB + 6303X + rom image. If you still want one to play with let me know. Not sure how to connect with you directly?
        best regards

  2. MartinM says:


    I disassembled Dynacord’s MIDI Rhythm Stick, that uses a 6303.
    Used dasmx to disassemble, some time to make it readable and
    dasm to produce an exact copy of Dynacord’s 2764 ROM.
    Meanwhile I am in the process of optimizing / extending the
    software to my personal needs.
    I could send the sources / files if that would help as helping each other is helpful 😉

  3. grantb4 says:

    That’s an interesting unit, I’d never heard of that before! I’ll have to investigate.

    Someone suggested using the MAME Debugger and that has piqued my interest too but have not had a chance to follow that up. Also there is an automotive ECU group that have a 6303 software emulator but I haven’t approached them yet either. I have done a bit of emulation on my PC with a Motorola 68hc11 emulator, that was somewhat helpful.

    I do like the idea of forward assembling to verify the content.

  4. grantb4 says:

    I would be happy to post/archive any files you would like to offer. And I can try and make a Monitor EPROM hex file that works in the target system. Because it uses the UART for terminal I/O that impacts the MIDI (understatement) and the single-step uses the lone internal timer. Mostly I just use the monitor for setting breakpoints or tracing through small sections of code.

  5. grantb4 says:

    I thought I should point out another great resource with some 6801/6803/6303 discussion:

    One of the commenters there talks about an IDE with a table driven assembler that can be custom tailored to the CPU of your choice. Here is the page that discusses MiniIDE and the Telemark Cross Assembler:

    And the document in question:

    Currently I’m using DASM:

  6. vintagechips says:

    I will introduce another option to those who need SBC6303 and so on. Seeed manufactures PCB at $4.9 for 10pcs. The surplus PCBs can be sold at a price suitable for Open source.

    I just uploaded Gerber data to Fusion gallery.
    Please visit Fusion gallery.

    The SBC series is a ‘loose kit’ that provides only PCB.
    Sorry, We can not support assembly.

  7. grantb4 says:

    Thank you! I will order 10 of each of these 3 boards.

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