More Out The Bank Manager - AMSTRAD cpc 6128 User Instruction

ChapterS
More out the Bank
anagerll
11 1111
Extensions to BASIC allowing access to the second 64K bank of
RAM.
Subjects covered:
*
Storing screen images
*
Pseudo-file operation
The memory map for BASIC 1.1 (shown in Chapter 7 part 14) indicates that 64K of
the 128K RAM is unused. The BASIC and firmware themselves reside in a ROM
which, together with the disc ROM, increase the normal memory provided from 64K
to 112K (64K RAM, 48K ROM).
Each section of16K is called a 'block', and any particular selection offour blocks (to
make 64K in total) is called a 'bank'. The technique of selecting blocks is therefore
called 'bank switching'.
The Z80 microprocessor can accomodate only 64K of memory at anyone time, so the
operating system contains instructions to switch the firmware ROM into play instead
of Block 0 of RAM, and to switch either the BASIC ROM or the disc ROM into play
instead of Block 3. This switching takes place automatically when the BASIC or
firmware is required. Bank switching of RAM merely extends this concept to include
the overlaying of RAM, rather than ROM. The switching is taken care of by an
assembler program.
The program BAN K M AN. BA S is provided on Side 1 of the system discs package. If
the program is run after BASIC has started, it will install the standard bank
management RSX code. Hence, the program is known as the 'BANK MANAGER'.
One use for the memory in the second 64K is as temporary storage space for picture
screens. Such applications may include, for example, a 'Screen Designer' program
which stores a number of different screens, or a video game which may have a number
of different screens already prepared.
Another use for the second 64K is as an extension to the variable workspace, which
can be regarded as either an extension to the string array space, or as a simple
'RAMdisc'.
More About the Bank Manager ....
Chapter 8 Page 1