SBC-85 1Mbit Memory Expansion Board

I have populated the newer v1.0a board which has latched strobes on the access LEDs.  It really depends on the LED but with a 100 ohm current limiting resistor general sequential access provides a nice flicker for the LED and full on fill or copy of the memory block provides a full-on glowing LED status.  I am sure it could be further improved but all-in-all the LEDs are just useful enough to bother populating but not so useful enough to that I want more of them.  The selection issues that were there when lots of 'don't cares' were in the address selection mask are now gone and the LED only flickers when that specific address block is being accessed.

I have toyed with the idea of adding a monostable that will keep the LED on for the full duration of the memory access, but i kind of like the varying levels of 'flickerness' that gives and indication as to the frequency of access.

I am calling the memory board at a stopping point so have uploaded the user's manual, BOM, and build files to the sbc-85 project website.

Version 1.0 of the memory expansion board has been built and all preliminary tests indicate it is good to go.  As seen in the photographs, the first test configuration has a 2732 EPROM, two 2764 EPROMs, and a 6264 RAM.  For more complete testing, I need to do more mixing and matching and use all versions of EPROMs up to the 27256 in various combinations.  In this test I have the two 2764s mapped at the same address space in different pages and that works well.  Some nice features on this board even if I do say so myself.  The addressing seems confusing at first but I think it is straight forward once explained.  I guess we will see when I start to get feedback on the [so far non-existent] documentation.

As a first step in the documentation, I did start to put together the cheat sheet for the board to help keep track of how it is configured.

Version 1.0 of the memory expansion board has been built and all preliminary tests indicate it is good to go.  As seen in the photographs, the first test configuration has a 2732 EPROM, two 2764 EPROMs, and a 6264 RAM.  For more complete testing, I need to do more mixing and matching and use all versions of EPROMs up to the 27256 in various combinations.  In this test I have the two 2764s mapped at the same address space in different pages and that works well.  Some nice features on this board even if I do say so myself.  The addressing seems confusing at first but I think it is straight forward once explained.  I guess we will see when I start to get feedback on the [so far non-existent] documentation.

As a first step in the documentation, I did start to put together the cheat sheet for the board to help keep track of how it is configured.