This blog is intended to document my effort toward the making a product of the Z79Forth concept. Back in January 2019, I started assembling a single board computer based on a very simple architecture. I targeted the Hitachi HD6309E, an evolution of the original Motorola MC6809E micro-processor and proceeded to develop a fully functional 8 bit computer. The basic hardware development process took about a month of off work of my time.


Like any other computer creation project, you have to start with the essentials: power, clocking, address decoding, essential I/Os, RAM and something that resembles a BIOS. From a hardware standpoint, the original feature list was as follows:


  • 8 KB EEPROM for resident software (a Forth 79 standard sub-set).
  • 32 KB SRAM, possibly extensible through an extension connector.
  • Asynchronous serial communications. From the very beginning, this was based on the HD63B50 ACIA (Asynchronous Communication Interface Adapter) coupled to an USB adapter for interactivity with the system and power supply purposes.

 

Later on, I added mass storage support through a CompactFlash interface. CompactFlash is a dream to interface to a computer's bus since it has its own integrated controller. My own implementation of it is the time tested 8 bit flavor. The original CF interface was a straight copy of Daniel Tufvsesson's. May he be hereby thanked for making his designs publicly available to anyone interested.


This began as a conceptual (research) project only. I presented the outcome of the project during a Forth2020 Zoom online meeting as a design only thing in May 2021. I later changed my mind and decided it would be quite a learning personal experience to build a product (a kit) based on the design. This blog is an attempt to document this endeavor.


From a software standpoint, I already had a serious basis to build on. Back in the summer of 1984, I had written a Forth implementation geared toward the computer I owned, back in the glory days: a Tandy Radio Shack TRS-80 model 1. The best software I ever got for that baby was Microsoft's EDTASM+. A line oriented editor/assembler with an integrated debugger. After about a year of toying with the thing, I came out with some software that was my understanding of the Forth 79-STANDARD. Of course, back then I was 19 and had no Internet access so my understanding was entirely based on a book: "Programmer en Forth" by Alain Pinaud. I managed to get in touch with the author somehow. To me, he is a legend as much as Rodnay Zaks is to a lot of folks. The software is dedicated to Alain.


Of course, reality's demands do not quite match the creative mind of a 19 year old boy and it turned out that standard compliance was not what the 1984 output had produced. The porting effort from the Z80 to the 6809 and the standard compliance effort is a long story that will deserve further coverage.



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