I mentioned in an earlier post that the first 8085 system I ever created was the Intel MCS-85 3-Chip Minimum System. This has the 8085, an 8755 I/O EPROM, and a 8156 I/O RAM. The capabilities of this minimum system blew my mind. My wire wrap version has long gone missing, so I decided to do a little updating and make myself a little feel-good retro project.
I doubt that many others have an interest in this platform, if for no other reason than it has a 8755 EPROM which not every hobbyist can program. I mentioned Matt Millman’s Arduino shield and 8755 adapters, and I have some in my next PCB order for those that want a set.
Anyway, back to the MCS-85 project–
I decided to do one little tweak to the board, well two actually. First I included a little space for a one-bit inverter so you can turn an 8155 into an 8156. That should save you a few dollars since the much more common 8155 is a few dollars cheaper than the 8156. The only difference, of course, is the logic level of the Chip Select, but try and talk to the wrong version and see how that goes.
The second little addition, and the reason I am calling this the MCS-85+, is I added in another Intel novelty chip, i.e., the 1K 8185 RAM. I expect little support for that decision. The 8185 was a bit of a white elephant (video) because it priced itself out of the market. However, they are reasonably available, and I have several on my shelf looking for a home. Besides, that extra 1K of RAM really makes the board sing.
If you happen to be interested in such things, I will make the build files available after I get the board in and tested.
Regards
-c
