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Fairchild F8 38P70 Development Platform

Creating a Development Platform for the Mostek 38P70 version of Fairchild's quirky little F8

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Someone sent me a couple of Mostek 38P70s with the challenge of making something useful. Challenge accepted, and a real time clock seemed like about the right speed for these chips. Top off the project with some DL2416 alphanumeric displays to make a 16 character super clock that will certainly have that nice 1970s vibe.

While it deserves a place of honor as the first microcomputer, the F8 is like no other.  The F8 internal structure borders on abstract, the instruction set is missing some of the most basic instructions, and it reeks as a product designed by committee and rushed to market.  Nonetheless, it is a piece of history that i didn't participate in at the time, so i wanted to be able to experience the F8 firsthand.  In order to learn about the F8 and its programming, i wanted an adequate development platform with the usual digital inputs, outputs, display, serial interface, etc.  The 100mm x 100mm board includes:

  • Pushbutton input
  • 4-bit rotary encoder
  • Speaker
  • LED
  • four DL2416 providing 16 digits of alphanumeric display
  • DS1302 real time clock
  • RS232 serial port
  • Onboard 555 to provide tick inputs to the external interrupt
  • Signal header

The board was designed to use Mostek's 2nd generation version of the F8, the 38P70 which are readily available in the $30-$50 range.  A piggyback 2716 EPROM provides ROM while the 38P70 includes its normal 64 bytes of scratchpad plus an additional 64 bytes of executable RAM

  • 1 × Mostek 38P70 F8 microprocessor
  • 4 × DL2416 Displays and Inverters / LED Displays

  • Build Files Available

    Craig07/18/2022 at 20:27 0 comments

    The board has been tested and build files are available here:

    SBC-3870 F8 Board Documentation » Bits Of The Golden Age

  • Hardware update--basic functions tested

    Craig05/10/2022 at 17:52 0 comments

    Board testing

    Boards are back from the fab house and i have partially populated to do some initial tests.  So far, everything is checking out OK.  I have tested the external interrupt, have been able to write to the displays, read/write the serial port, read/write to the RTC, read/write to the digital I/O (switches, LED, speaker).

    Display dimming

    Has anyone successfully dimmed the 2416 display across any meaningful range? While waiting for the boards, using a function generator i tested PWM dimming on some of my DL2416s and found that none of my Litronix versions of the display appreciate the dimming signal.  I could not find a frequency that would uniformly dim the display and most frequency ranges really messed with the internal refresh clock.  So I do not plan on even populating the dimming circuit unless i can get my hands on some other manufacturers' 2416.  The dimming may work with the newer 5x7 matrix display but i have not tried.

    Software

    i am using the DASM assembler which, despite it's limitations, has provided functional code for board testing.  If anyone knows of a more capable assembler for the F8, please let me know. 

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