Johnny's homebuilt 8080 CPU corner (and other stuff, maybe)
This card holds both SRAM and ROM.
The SRAM part are a 512K chip, wasting away lot of usefull RAM but that was what I had on hand when I designed the board.
The ROM part are a parallel FRAM 8K memory from Ramtron. It's an old chip but available from Ebay and AliExpress.
Using a FRAM memory simplifies the process of updatering the ROM section a lot - I can write new code to it by closing a jumper, instead of having to rip the ROM from the board and use a separate programmer.
Moreover, this FRAM memory can also be written to directly from the 8080 itself, if necessary.
This version of the memory board do not support bank switching.
The FRAM has a special timing requirement to accept writing information to it, but fortunately I, by pure luck, happened to built that into the 8080 memory handler from the beginning. FRAM where not on the table at that time.
There are a jumper to select how much FRAM/ROM memory to use at the bottom of the 64K memory space, the rest are filled in by the SRAM chip.
On the top right there are a manual jumper that has to be closed to allow write access to the FRAM, in conjuction with the write protection circuit.
To join the Homebuilt CPUs ring, drop Warren a line, mentioning your page's URL. He'll then add it to the list.
You will need to copy this code fragment into your page (or reference it.)
Note: The ring is chartered for projects that include a home-built CPU. It can emulate a commercial part, that′s OK.
But actually using that commercial CPU doesn′t rate. Likewise, the project must have been at least partially built: pure paper designs don′t rate either.
It can be built using any technology you like, from relays to FPGAs.