83:OS:Memory Mapping

From WikiTI
Jump to: navigation, search

Memory Mapping

Memory on the TI83 has been split up in 16Kb pages. The 256Kb of ROM has been split up in 16 such pages. The 32Kb of RAM have been split up in 2 pages.

The following table describes how these pages are mapped to the 16 bit address space of the z80 depending on the value of various I/O ports.

Port 04 bit 0 Port 02 bit 6 Port 02 bit 7 Port 02 bit 3 0x0000 0x4000 0x8000 0xC000
0 * 0 0 ROM0 SWAP ROM0/8 RAM0
0*01 ROM0 SWAP ROM1/9 RAM0
0*10 ROM0 SWAP RAM0 RAM0
0*11 ROM0 SWAP RAM1 RAM0
1 0 0 0 ROM0 ROM0/8 SWAP ROM0/8
1001 ROM0 ROM0/8 SWAP ROM1/9
1010 ROM0 ROM0/8 SWAP RAM0
1011 ROM0 ROM0/8 SWAP RAM1
1 1 0 0 ROM0 RAM0 RAM1 ROM0/8
1101 ROM0 RAM0 RAM1 ROM1/9
1110 ROM0 RAM0 RAM1 RAM0
1111 ROM0 RAM0 RAM1 RAM1

The line in italics is the default mode.