I'm writting like newbie, but have not clear how to use external ROM. Internal ROM has free U36 socket and this makes it easy to use.
What I know that REU 1700 and 1750 can have socket - but must to be soldered in, or? I own upgraded REU 1764 up to 1536K (1,5MB) and have not free socket place and even 1764 was designed for C64 so don't know if it can work anyway.
Exist any other way where to place external ROM?
Thank you for help. Miro
Commodore 64 was great, Commodore 128 is bigger, better, faster and more powerful... Commodore 65 was almost here, but C256 is coming and it will be earthquake...
I'm pretty sure that using the external ROMs (i.e., a normal C128 cartridge) from the cart port lines is a matter of MMU configuration. It's been a long time since I even cared to look at this topic, but I believe there are preconfigured MMU bank settings that function just like the ones for the internal function ROM except they deal with external function ROM instead.
An external cartridge is referred as “External(Function ROM)” and the internal EPROM socket is referred as “Internal(Function ROM)”. This will focus on how to create an external cartridge.
There are two areas in the C128 memory where cartridges can be located; the MID ($8000-$BFFF) and HIGH ($C000-FFFF). A cartridge can be started up in either these 16K areas or single 32K cartridge can be used. It is possible to have both an internal “cartridge” and an external cartridge installed, but the external has preference over the internal.
C128 memory is managed by a chip called the Memory Management Unit(MMU) and does not use the PLA(GAME/EXROM lines) like the C64.
There should be alot more information on the net regarding this topic, but we can fill this thread with that info as time allows.
Banking description of Internal and External Function ROMs .. from Compute! (I hope this OCR'ed well.) Banks 4-7 feature RAM from banks 0-3, respectively, in the lower 32K of memory and internal function ROM—plus the I/O chips—in the upper 32K. Internal function ROM is Commodore's designation for the ROM which occupies a free chip socket on the 128's circuit board. This is a throwback to Commodore's original PET designs, which included empty ROM sockets for users to add their own special features. Right now the socket is empty, and locations $8000-$CFFF and $E000-$FF00 in these banks show only randomly fluctuating values. Until someone introduces ROMs for this socket, you can ignore banks 4-7.
Banks 8-11 are the same as banks 4-7, except that the upper 32K of address space contains external function ROM, the designation for ROM on a cartridge plugged into the memory expansion port. Like the empty internal ROM socket in -- banks 4-7, locations $8000-$CFFF and $E000-$FF00 in banks 8-11 show random and unstable values if no cartridge ROM is present. Thus, banks 8-11 can be ignored unless you have an cartridge you wish to use. This applies only to 128 cartridges: Plugging a Commodore 64 cartridge into the port forces the system into 64 mode.