Posted By
TLC
on 2011-06-21
12:22:39
|  Re: Plus/4 - PAL/NTSC switchable mod
Vimfuego: the majority of the connections are ROM CS' lines, the rest are probably R/W', CAS', and some other control signals. In short, the board has been a "prototype" of a universal 128k flash module ("universal" = it'd emulate 8 pieces of 16k ROM slices, ie. the ROM size decoded/mapped by the standard ROM CS' logics of the Plus/4). You can connect a maximum of 8 ROM CS' signals to the board from the mainboard and/or your own TTL logics. For example, in this C16 all original ROMs were just replaced by this single flash chip ie. the pages of the flash acted as Basic, Kernal, and the extra NTSC kernal (...and even the 3-plus-1 function roms originally only present in the Plus/4). A TTL priority encoder chip (which is located under the flash rom) encodes the individual ROM CS' lines into a 3-bit page address ie. the highest 3 bits of the address which is then fed to the flash chip. The rest were needed by the in-system-programmability function (ie. you could rewrite any pages of the flash chip using a small ML routine without removing the chip from the socket). ...It just ended up like yet another prototype that never really "made it"  , but it became handy (at least, for this hack) nevertheless...
|
