EBTKS - HP85A/B Tape Drive Replacement

Bringing HP Series80 computers (HP85A/B et al) back to life and a great upgrade

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The HP85A desktop computer was introduced in 1980 around the same time as the first IBM PC. It included a processor, 32 kB ROM BASIC, 16 kB RAM, 32 character by 16 line CRT, keyboard, printer, and tape drive. Search eBay for lots of pics. There is an active community of aficionados that continue to use these computers. Unfortunately the rubber capstan in the tape drives of pretty much all of these computers has either disintegrated or turned into goo. No spare parts are available, and repairing the capstan is quite difficult. The tapes aren't made any more and even new old stock (NOS) tapes are unusable, as their rubber drive belts have bonded to the oxide on the tape. As soon as the tape is moved in the cartridge, it is destroyed. EBTKS is a plug in module that emulates the tape drive and provides 20,000 virtual tapes. Once the project started, we realized that with more software effort the board could do far more. See below for a full feature list.

Although EBTKS started out as just a solid state replacement for the failing tape drives, its capabilities have expanded far beyond the original goal.

The Features include the following:

  • Tape drive emulation, using the 16 GB SD card to store Tape images. Theoretically the SD card could hold about 200,000 tape images. To use this service, the existing tape drive must be disabled by unplugging the two flat-flex cables.
  • Disk drive emulation, using the 16 GB SD card to store Disk images. The number of disk images will depend on whether the emulated disk is a floppy or Winchester disk drive. We hope to support multiple disk drive types.
  • RAM to fill the top 16 kB of the HP-85A.
  • Up to 256 kB of Extended memory for HP85B (EDISK), and HP86/87 computers
  • EBTKS provides for up to 18 ROMs to be loaded from the SD card under control of the CONFIG.TXT file. Due to constraints imposed by the System ROMs, only 14 option ROMs are supported (one is system ROM 0). This is sufficient for all 12 standard published Option ROMs. The remainder of the 18 ROMs use a special facility for AUXROMs, discussed later. Currently there are four required AUXROMs which specifically supports EBTKS.
  • No Jumper configuration. Configuration of options (like which ROMs are active, initial tape/disk image loaded) is under control of an easily editable CONFIG.TXT file on the SD card.
  • Direct access to the CRT to move cursor and read/write text
  • Improved auto-start program can include multiple commands or a simple batch file.
  • Only requires 1 slot in the I/O backplane
  • HELP facility (still in development)
  • Diagnostic console using serial-over-USB
  • Other features are still in development
  • Over 70 New Keywords that include file management, directory management, direct read and write of the SD card with Posix like functions, utility functions to import and export files using GET/SAVE functionality, sprintf() string formatting, and more...
  • Hierarchical File System (FAT32 style) that supports long file names, long sub-directory names, and nested sub-directories
  • Open source software, can be reviewed now on GitHub
  • Open source hardware after the first production batch is shipped
  • Coordinated compatibility with Everett's Series 80 Emulator.

For now (and for the future) the best place for the documentation is the link on the left. All the source code is on GitHub.

  • 1 × Teensy 4.1 Microprocessor module from PJRC
  • 3 × SN74LVC8T245PWR Logic ICs / Receivers, Transceivers. Use for its level shifting capability
  • 1 × CD4050 Level shifter. The HP85 computers uses a 4 phase 12 V clock system.
  • 1 × ESP32-Wroom-32D Added WiFi, because why not
  • 2 × WS2812B RGB LEDs because computers need flashing lights

View all 6 components

  • Pointers to where the documentation is and the team

    Philip06/16/2021 at 12:00 0 comments

    All of the documentation is can be found here

    The team is Philip Freidin, Russell Bull, and Everett Kaser. We have been working almost non stop on this project since early 2020, so the Stay At Home situation actually helped put more focus on the project as we had reduced distractions.

    The project got to its initial launch almost exactly at the same time as the Hackaday Reinvented Retro competition was launched, so this should be a great fit.

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