OMEN Alpha: A DIY 8085-Based Computer

8085-based single board computer

[Martin Malý] has put together a sweet little 8085-based single board computer called OMEN. He needed a simple one for educational purposes, and judging by the schematic we think he’s succeeded.

Now in its fourth iteration, it has a 32K EEPROM, 32K of memory, one serial and three parallel ports. In the ROM he’s put Tiny BASIC and Dave Dunfield’s MON85 Serial Monitor with Roman Borik’s improvements. His early demos include the obligatory blinking LED, playing 8-bit music to a speaker, and also a 7-segment LED display with a hexadecimal keyboard. There is also a system connector which allows you to connect a keyboard, a display, and other peripherals. Of course, you can connect serially at up to 115200 baud, making it very easy to compile some assembly on a PC and use the monitor to paste the hex into the board’s memory and run it. Or you can just jump into the Tiny BASIC interpreter and have some nostalgic fun. He demos all this in the video below.

He’s given enough detail for you to make your own and he also has the boards available in kit form on Tindie for a very reasonable price. With some minimal soldering skills, you can be back in the ’80s in no time.

Part of [Martin’s] interest in these vintage computers stems from his having grown up in the ’80s in Eastern Europe when it was impossible for him to have a computer of his own. We’re glad then that he wrote up his experience with home computers behind the iron curtain as well as the peripherals.

22 thoughts on “OMEN Alpha: A DIY 8085-Based Computer

    1. Hello, I am sorry for “sold out”. The new components are on its way (PCBs arrived yesterday, now I am waiting for 28C256 EEPROMs), but I hope I can offer 10 sets until the end of the week. Please leave your contact in a wait list on Tindie to stay informed. Now I am really happy about the interest, so I offer my only completed piece to buy (yes, the second live prototype). Thank you…

  1. I have a dozen old boards from serial terminals in my junk boxes with 8085 chips and a variety of the support chips from that era. I guess I should get busy and put those up on Ebay.

  2. Interesting… I found a presumably brand new 8085 (In a little blister pack) the other day and was wondering about making an 8 bit box with it… I kinda want something CP/M native to screw with though, I see it’s meant to have 8080 instructions but haven’t particularly noticed people running CP/M on them. Was looking at that Z80 proj that uses an atmel 328 for support chip fudgery.

  3. Intel published the code for using SID and SOD todo serial I/O, it’s all about the specific clock frequency , just have to run the DI instruction . Cant remember was it an ASCII A, or space to get the timing count?

  4. I built a vehicle performance monitor around a 8085, UV EEPROM, SRAM, a floating point math coprocessor, those dot matrix displays and a commercial 3 axis accelerometer. Fairly heady stuff for 1988! Did inertial navigation calculations to determine 0-30, 0-60, braking distance, corner G’s and of course the 1/4 mile time and speed. All wire wrap and assembly code! Those were the days.

  5. The 8085 was the first microprocessor I touched. I spent a good man-year writing assembly code for those things. That was an exciting time.

    However, it was a nightmare just getting everything running. You need a moderate board full of chips to duplicate what you get on a basic microcontroller. I think we sometimes forget just how bad the “good old days” were.

  6. Yes, the “good old days” were pretty bad sometimes. Just thinking about erasing and burning proms while debugging should bring a dose of reality to those misty eyed memories. These kids today take in-circuit programmable flash for granted.

  7. I’m curious why you chose the 8085 over the Z80. I’ve used both extensively, and with the Z80’s extra registers and the block move instructions, you have an advantage. Was it just a special spot in your heart for the 8085, parts that were laying around, or some other reason?

  8. I love the 8085 very much, it can do about anything, running at 6.14MHZ /2. What I don’t get is why the serial I/O chip is not interrupt driven. i doubt 115kbs can be polled. My design runs at 4MHZ/2,, inverts the rs232 transciever chip out, generates a RST 6.5, reads the SID, can handle 4800kbs no problem

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