On Sat, Dec 19, 2020, 2:38 PM Scott McDonnell <mcdonnell.j...@comcast.net> wrote:
> Now that I have proven out that a 27C256 EPROM is working fine in this > one, I am going to play around with customizing it. The real ULTIMATE would > be to replace the ROM with an EEPROM (like 28C256) and add in some type of > loader where you could update the main firmware over serial. That may not > be possible because often in these 80’s computers they usually placed some > IO address space in the ROM area (since write is not possible to the ROM) > and decoded it using the write signal and address. It was a simple trick > for accessing output only IO. I am talking out of my rear end right now > because I haven’t studied the schematic/memory map in detail yet. > http://tandy.wiki/FlexROM_100 http://tandy.wiki/FlexROM_102 Especially in concert with REX Classic http://tandy.wiki/Building_a_REX or arcadeshopper.com sometimes has rex classic pre-built you can just buy. You'd use the FlexROM_102 in the 100 that has the standard pinout. If you don't care about using the fully software loadable main rom via REX, and only need a plain 28C256 to 27C256 adapter without the /CS breakout remote loop, this would be a bit more convenient because it doesn't need a soic-28 test clip to program it. http://tandy.wiki/28C256_to_27C256 You just switch a couple jumpers and pop the board right in the programmer. >
