A new beginning
I plan on using this blog to document my newest project. I found with the last project, documentation after the fact is more difficult than I thought it would be. I have a hard time remembering why I did some things the way that I did.
The last project was using a Xilinx Spartan 3 FPGA board to build an Ohio Scientific Superboard / C1P with Verilog. I have finished this project. I left a few hooks in the code to add Apple functionality also. My plan is to have it boot OSI / Apple depending on a switch setting. Since the FPGA is just over 50% full there should be ample room for the Apple functionality. Of course, the CPU code and UART code will be common. I just need to add the Apple specific memory map, video, keyboard, and whatever.
The first decision I need to make is the Apple model to build. Since the CPU code has only the NMOS instructions completed, this somewhat limits the options. The Apple //c and enhanced Apple //e are not options. The un-enhanced Apple //e seems to be the logical candidate. At first the additional memory management seemed to be too much. But since the Xilinx board has 1 Meg of memory, I might as well use as much of it as possible. I plan on using 128K of one of the two 512k chips for the main memory and aux memory. The other 512k chip can be used for a memory expansion board like I used to have on my //e. If I can find the technical specifications and ROM code for this board.
One issue that I have to address is the ROM space. Since the OSI ROMS take almost all the internal FPGA ROM / RAM space, I need to interface some other ROM / RAM memory devices. I also want to make some of this appear to be a standard 5.25 inch floppy. I think this is a difficult task, but not impossible. It may require the ROM to be loaded into RAM and then written back to ROM when needed because of the way the Flash programming operates.
The biggest issue that I see now is information. When I had my Apple ][ and Apple //e, I know most of what I now need to know. But since it has been many years ago that I stopped using them, I have forgotten this information. Some of it I can get from the schematics, some of it I can get from source code for the emulators, and hopefully I can download the remaining information from somewhere on the internet.
The "Plan of Record"
Un-enhanced Apple //e
128K + 512K memory board
40/80 character text video
High resolution graphics
(maybe double HGR)
RGB (VGA) monitor support
Super Serial Card
PS/2 keyboard that appears
to be a standard keyboard to the system
Real Time Clock (TBD)
Some type of support for standard 5.25 inch floppy