Multifunction companion board
for the Spare Time Gizmo's SBC6120

Hardware emulation of numerous DEC PDP-8 options, and lots more!

  • CompactFlash™ interface

  • 2MB nonvolatile ramdisk

  • VT52 terminal with output to a standard VGA monitor and input from a standard PS/2 PC keyboard.  The VT52 can be set as the console device by a jumper, and the SBC6120 serial port becomes another SLU.

  • 3 serial ports (SLUs) compatible with DEC KL8JA (RS232C)

  • Printer Port compatible with DEC LC8E with buffered Centronics parallel output

  • Crystal Clock DEC compatible timer device

  • 36 digital I/O pins that can be individually configured as inputs or outputs

  • Complete Flexibility due to its FPGA implementation; IOB functions may be enhanced, removed, replaced or added.  For example additional serial ports or a front panel interface could replace some of the digital I/O pins.  Using free Xilinx VHDL synthesis software, the 100K-gate FPGA's programming can be altered and tested. Currently, only 70% of the device is used for all the functions listed here.

  • Flash ROM used to store OS extensions and FPGA programming; 128-384KB free for other uses.

  • Clock/calendar (optional) battery-backed year/month/day hour:minute:second clock

  • Speaker (audible bell)

  • Enhancements to BTS6120 (see below)

Here is the manual in PDF, and here are the design, software and documentation files: current_version (~1.8MB).
(the filename of the current version reflects the BTS6120 version, the extension ROM version and the FPGA code version)
This device's design is made available under the terms of the GPL.

There is lots of reusable, fairly modular VHDL IP in there - a configurable UART, PS/2 keyboard to ASCII, ASCII to VGA video, serial terminal and other good stuff.  It's mostly wrapped in code that interfaces it to a PDP-8 bus via IOT's, but it's not specific to that bus.

The construction of the board is straight-forward, but since it is built with surface mount components, good  tools and some practice are strongly recommended before tackling it.  Most parts are half pitch (0.05" lead spacing), and are easily solderable with a fine-tipped temperature controlled iron and fine solder.  A few parts are fine pitch (0.5mm lead spacing) and can be difficult to solder without strong magnification and a steady hand.

I am no longer able to supply kits, parts or assembled units.
However, some people in the Yahoo SpareTimeGizmos group have built a new version of IOB-6120; please enquire there.

Changes and Enhancements to BTS6120

These are implemented in the revised SBC6120 EPROM set, and are useful even without an IOB6120.  The revised EPROMs are larger than the originals, so 27C256 or 27C512 EPROMS must be used instead of the 27C64's that were originally specified.