TRM: Memory - fvdhoef/aquarius-plus GitHub Wiki
[!WARNING] BASIC programs (machine language subroutines) should never write to the memory banking I/O ports. The plusBASIC interpreter requires memory to be in a specific configuration and will crash if the expected RAM page is not mapped into each memory bank. plusBASIC automatically manages page swapping and all memory related statements and functions have options to access paged RAM.
Memory Banks
There are 4 banks of 16k of ram available to the z80’s address space. Each of of four banks can be independently switched out to point at different 16k portions of the 512k of ram.
| Bank | Hexadecimal | Decimal | I/O Port | Hex |
|---|---|---|---|---|
| 0 | $0000 - $3FFF | 0 - 16383 | 240 | $F0 |
| 1 | $4000 - $7FFF | 16384 - 32767 | 241 | $F1 |
| 2 | $8000 - $BFFF | 32768 - 49151 | 242 | $F2 |
| 3 | $C000 - $FFFF | 49152 - 65535 | 243 | $F3 |
Memory Pages
| Page | Hex | Description |
|---|---|---|
| 0 | $00 | Startup ROM |
| 1 - 18 | $01 - $12 | Undefined |
| 19 | $13 | Cartridge port |
| 20 | $14 | Video RAM |
| 21 | $15 | Character RAM |
| 22 - 31 | $16 - $1F | Reserved |
| 32 - 63 | $20 - $3F | 512KB RAM |
- Pages 32 through 47 is User RAM and is free for use by BASIC programs.
- Pages 48 through 63 is reserved for plusBASIC and is read-only from BASIC programs.
plusBASIC RAM Allocation
| Page | Hex | Description |
|---|---|---|
| 48 | $32 | Reserved |
| 49 | $32 | Reserved |
| 50 | $32 | Transient buffers |
| 51 | $33 | Boot ROM work area |
| 52 | $34 | Screen buffers |
| 53 | $35 | Video RAM shadow buffer |
| 54 | $36 | plusBASIC system buffers |
| 55 | $37 | PT3 Player code and data |
| 56 | $38 | Bank 0 RAM |
| 57 | $39 | Bank 1 RAM |
| 58 | $3A | Bank 2 RAM |
| 59 | $3B | Bank 3 RAM |
| 60 | $3C | Main System ROM |
| 61 | $3D | Extended System ROM |
| 62 | $3E | Auxiliary System ROM |
| 63 | $3F | Cartridge Image |