What is it?

The MiniMax8085 project has been brewing for almost three years. In the spring of 2014 my kids and I visited a local surplus store, where my kids found some Intel 8000 series parts in the kids-fill-your-bucket area. Among these ICs were there: an 8085 CPU, an 8155 RAM with I/O ports and timer, a couple of 8255 PPIs, an 8282 latch, and some 27C128 UV EPROMs. It looked like a good start for an 8085 based computer that can be used to teach my kids some computer design and programming basics. I wanted the project to be simple to build, with a minimal number of components, but yet to be a fully functional single board computer (e.g. to include the memory and an input/output device, for example a UART) with an extension bus. I checked the Internet for existing homebrew 8085 computers and found Roman Fülek's NCB85 and NCB85v2 projects, and Glitch Works 8085 projects. While I liked these projects, they didn't quite meet my project design goals:

NCB85 was the closest, but it doesn't have an extension bus NCB85v2 is a little bit too complicated for my needs Glitch Works 8085 project didn't have an on-board UART The resulting design includes 8085 CPU, 8251 USART, 32 KiB SRAM, 32 KiB or 16 KiB ROM. It uses a GAL16V8/ATF16V8 simple programmable logic device (SPLD) instead of discrete logic ICs for the address decode and the frequency divider for USART. It reduces the number of components, allows for tweaking the configuration by re-programming the SPLD, and provides an introduction to the programmable logic devices.

Why did you make it?

What makes it special?

80C85A or 8085A CPU, 3.072 MHz, 4 MHz, 4.9152 MHz, 6.144 MHz, or 8 MHz CPU clock frequency 82C51A or 8251A USART for console connection 32 KiB of battery backed SRAM Up to 32 KiB of ROM. EEPROM, UV EPROM or Flash ROM memory is supported 40-pin extension bus connector, including most of 8085 signals and demultiplexed data and address buses