Single Board Computer

• Discrete I/O Board: Utilizes 4 each ULN2803 50V 500mA open-collector output driver IC's. Eight drivers on each IC provides 32 total Discrete Output points. I use 2 each 1K-ohm x 8 resistor pull-up packs tied to the 5V supply off the board. This gives me 16 Discrete switch inputs, which are high (logic 1) when the switch is open. I currently use this board to drive 28V "discrete input and outputs" on control panels at my work desk, makes a good test-bed.

• Memory Expansion Board: Completed April 2005, this board added two 32K non-volatile static rams and capacity for 4 each 2732 roms. The memory is bank switched using jumper pins. The fourth Rom socket is jumper selectable to hold either a 6116 Static Ram or a 2732 4Kx8 Eprom.

  Note: This board is under revision at this time, hopefully to incorporate bank-switching for CP/M and a CF card interface for hard-drive simulation.

• HD44740 LCD Display 2 x 40: I have also tied this 2x40 ASCII character display in using the 9511/12 socket at IC-17.
  This is an LED-backlit device which uses a negative 2Volts for biasing. Mine was $6.00 from BG Micro.
  I have built a special timing circuit using a 74LS175 which allows me to:

  • Read and Write the HD44780 as a directly mapped standard I/O device
  • Provide the -2.0Vdc bias voltage for the glass
  • Display the data bytes to and from the LCD using latched LED's
  IC-17 was designed for the AMD9511/12 floating point Mathbox. Since they are obsolete and difficult to find, it was the ideal place for this LCD Interface board as it has WAIT-, CLK, AB0, DB0-7, CS-, and both +12 and +5 available, as well as spare pins for -12V. This interface works significantly better than tying the LCD onto 8255 PIO, and saves those pins for other purposes.

  This was a temporary offering - This company has lots and lots of great electronic deals that come through there. Check back often for runs of new stuff.

• Monitor Rom: I have added various features and functions to the original Monitor program, as follows:

  • Rev 8.1
  • Jumps the baud rate up to 38,400 for the console Serial A [reqs new xtal].
  • Sets Serial B at 31,250 Baud for MIDI data.
  • Has ANSI color sequences for changing text color on-the-fly with Hyperterminal.
  • Initializes all devices on bootup, including the HD44780 LCD.
  • Generates ROM checksums on bootup.
  • Has a CP/M-like multi-device output print command.

  I have developed a version of the monitor program that works strictly with my 8279 Keyboard/Display controller and the HD44780 LCD display. I'm calling this one "Release 1.1" as it's been thru a few mods. It offers some simple functions:

  • Display Memory
  • Edit Memory
  • Input from port
  • Output to port
  • Clear Memory and I/O
  • Disassemble Memory (to serial port for capture)
  • Hex Math - AND,OR, ADD, SUB, and XOR for 16-bit Hex numbers
  • Load and Save - Intel Hex or .NAS Nascom format files

  I incorporated the .NAS format, which is essentially an ASCII text file format, in order to load files written to run on the Nascom computer and disassemble them. The Intel Hex format is the principal load/save format I use, as the Z80 TASM Assembler program outputs a nice Intel Hex output file for load or burning to eprom.

• MIDI Interface for Serial B port: See the menu for how I created an opto-isolated circuit for connecting MIDI devices. I have acquired a MOS 6581 CBM synthesizer IC [from the Commodore C64 computer], and am planning a music synthesis circuit board as a future add-in.

• Front Panel: I was able to salvage about 36 professional LED-lighted switches and 9 green and 9 red indicators (which also look exactly like the switches) off of some old equipment. They are top-quality devices and would probably have cost me about $6.00USD each new. Had new 19" rack panel milled-out by a friend. Completed the interface PCB and am in the middle of code and test. The control gained by this will give some monitor functions without a host PC, and will primarily be to interact with the MIDI and 6251 SID music synthesizer IC. See the pics on the 8279 Panel page, I think you'll like it.

While I like to believe that the possibilities are just about boundless, let me just preface everything by saying that you have to be a hobbyist on the level of enjoying things that work down to the bit level and one who likes vintage technology to get the sense of fulfillment that I have from this project. It can be all-consuming, and you should be prepared to funnel some funds and plenty of hours of research and soldering into it.

Here are a few things the users have done:

• Robotics One person combined the services of this board to an S-100 Z80 board to control his life-size R2-D2 robot!
• Model Railroads As a controller to animate, control motion and lighting based on where the train is in the layout.
• Christmas Lights To send flashy sequences to light strings by way of Solid State Relays.
• Process Control To control sequences on a machine based on position switch inputs (assembly line stuff).
• Education Probably one of its strongest selling points, to teach Z80 machine language, circuitry, I/O and the old BASIC computer language.

Here are some ideas that I have.
Some of these I've completed, others are in work or waiting in the wings:

• BSA Pinewood Derby As a race controller to sequence the 'tree', pull in the car-blocking solenoids and to time the cars as well as determine the winner.
• MIDI Filtering To take in canned MIDI files and filter out the Track 10 "Percussion" track before it hits the keyboard.
• MIDI Instrument To read in switches or key-hits and convert them to a MIDI stream for driving keyboard or drum machine.
• MIDI Light Controller To allow stage lights or special effects displays to be synchronized to music.
• SID Synthesizer To drive the Commodore 64 "SID" chip and take MIDI data out to it.
• Church Chimes There is a local church whose paper-roll-driven chime machine is long dead (mid 1950's). I'd like to build a MIDI receiver that would use the 8255 outputs to strike the chimes based on which note was being played and resurrect this machine.
• CP/M Computer I've always wanted to hook a CF card into my Z80 computer and make it run some older games and software.

In December 2009, I noted that Rodnay Zaks' "How to Program the Z80" book has been made available for free download. Follow the link provided earlier.

Also made available the preceeding link to Steve Ciarcia's book "Build Your Own Z80 Computer".

Can I still get these boards?

Alert reader David Ray noted some of these for sale on eBay January 2011: LINK HERE. They are the bare board and monitor rom ONLY, although other chips are in the photo.

Michael Lee Simon, designer and producer of this board, is on Facebook. You can visit with him as he has several boards and various items laying around his shop.

Sorry, but I only have a couple of these boards around in various states of progress. I wish I had more, I'd certainly sell any I could get my hands on.

Notes:

If you own one of these computers, please take a moment to email me.
Also, I'm interested in what you are doing with your Space-Time Productions computer, and would like to include that information in my website. Photos are welcome as well.

ALSO: If you bought one of these boards a while back and aren't using it, please contact me. They are increasingly rare and the IC's that were sold in the kits, such as the Z80 SIO and the Intel P8279, P8253 and P8255 chips are pretty useful, too. Thanks!

Are you missing some chips for your Space-Time computer? I have a wealth of DIP type IC's, several Z80 CPU's, 74LSxx series logic, the resistor network DIP, plenty of 2732 4Kx8 Eproms if you need your program burned onto a chip just for your particular application - Let me know!