Posted By
SVS
on 2015-02-16
12:32:16
 |  Re: Bankswitching of Plussy and its programming
Hi Miro,
summarizing, the Plus4 has 32K+32K of RAM and 32K of ROM online.
The RAM bank "hi" stands from $8000 to $FFFF, but the ROM too, as explained by Litwr. It is said "the RAM under the ROM".
If a program writes to a byte in that area, no problem: the value is stored in the RAM. On the contrary to read a byte there needs to set if you want read RAM or ROM (since the address is the same). The flag of TED map makes the work.
Not the whole RAM high bank is available for user. Some areas are always dedicated to ROM (I/O, TED, long jump routines, etc.). This is why Basic welcome string says 60K and not 64K free.
This is the operating way between ROM/RAM switching. If you are interested into RAM expansion operating (like 256K expansion) I can write you more.
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