The first single board computer that I wire wrapped was the Intel 3-chip MCS-85 minimum system with an 8085 CPU, a 8156 RAM + I/O, and a 8755 EPROM and I/O. The second that I wire-wrapped was a SDK-85 that I thought would be a great Christmas present for [who is now] the Mrs. (As it turns out, she wasn’t as excited about the SDK085 as I was).
My homemade SDK-85 not only taught me the 8085, but it taught me a lot about selecting presents for the Mrs.
I had a great fondness for those boards. so sometime later i turned these little wire-wrap creations into real circuit boards, but sometime over the last 40 or so years these have all [mysteriously] gone missing and I have given up on ever finding my beloved original wire wrapped boards or their PCB versions.
I have thought about bring them back and sharing the project, but these rely on the 8755 EPROM and, as you may know, not every grandmother has an 8755 programmer. My Needham EMP-20 remains my workhorse for the 8755 (and MCS-48 projects) but not everyone is so fortunate to have one of these. I had started recreating these boards as (yet another) back burner project, but because these boards require the 8755 and most can’t program that chip, I wasn’t considering adding them to the SBC-85 family of shared projects.
However, recently I came across Matt Millman’s project page for his MCS-85 Arduino shield and adapter board for the 8755 which is making me reconsider finishing these out as SBC-85.COM projects.
As I remember the minimum system board, my version had the 8085, 8156, and 8755, but it also had a socket for the Intel 8185 1KB RAM.
My original wire-wrapped was a single board, but the PCB version of my SDK-85+ was a two board system, one was the keyboard and display and the other the main board. Like the original Intel SDK-85, my main board had an 8085, a pair of 8155s, and a pair of 8755s so it could run the original Intel SDK-85 resident monitor. But I also added a couple of EPROM sockets and sockets for one or two 8185 RAMs if i could ever afford them (I don’t remember if the 8185s were ever populated actually).
I used a much improved resident monitor on my SDK85 that used a terminal for disassembly, changing registers, etc., so the keyboard / display wasn’t required like the original SDK. Nonetheless, the displays and keypad were great for program input and display. An especially fun project that I remember, was learning to program programming the 8279 keyboard / display controller to create a musical piano / organ keyboard. Is it any wonder why we reminisce about those days of simple challenges and simple accomplishments?
Since I needed to start the boards from scratch, I have decided to update some components and change the EPROMs to universal sockets and add a MAX232 so I could drop the +/- 12V power supply. I also added a few more keys to the keypad and a few more digits to the display. If you prefer, you can break the display at the tab and put on little hinges to make it easier to view or panel mount. Other than that, as best as I can remember them, I think that I have pretty much stuck to my original design.
The keypad / display board has the 8279 keyboard / display controller and three Vishay TDC 0.39″ Quad Display Modules for a total of 12 digits.
the main CPU board and the (optional) keypad / display board use a short IDC ribbon cable, but you could put in straight M/F headers and directly plug the boards together I suppose.
These are still a back burner project for me and I don’t know when they will get finished and off to the PCB house. But if you miss having the 8755 on your bench, maybe these would be projects of interest to you? Let me know!