4 Chapter 2: TI-83 Plus Specific Information
TI-83 Plus Developer Guide Third Release May 28, 2002
HARDWARE LAYER
Loading and debugging an application requires a general understanding of the memory
layout of the calculator.
Other manuals and guides cover TI-83 Plus operation including keys, screens, menus,
etc. This discussion covers the TI-83 Plus internal hardware components —
Zilog Z80™ CPU, RAM, and Flash ROM.
Z80 CPU and Memory
The TI-83 Plus uses a Z80 processor with a 64K byte logical address space. To provide
more than 64K bytes of physical RAM, this logical memory space is divided into four
16K byte pages (see Fig. 2.3). Physical memory is also divided into two 16K byte pages
(see Fig. 2.3), and a physical page is mapped into each logical page as it is needed.
There are two types of physical memory in the calculator — Z80 RAM and Flash ROM.
The following sections address the composition, structure, and uses of these memory
types.
• Z80 Logical Memory Space
The Z80 logical memory size is 64K bytes, which is divided into four 16K byte
pages — 0000h to 3FFFh, 4000h to 7FFFh, 8000h to BFFFh, and C000h to FFFFh.
A physical memory page is mapped into each logical page.
FFFFh
0000h
4000h
8000h
C000h
3FFFh
7FFFh
BFFFh
16K Always RAM Page 0
16K RAM Page 0,1 or Flash ROM Pages 0-31
16K RAM Page 0,1 or Flash ROM Pages 0-31
16K Always Flash ROM Page 0
Fig. 2.3: Z80 Memory Space
The 16K byte address space from 0000h to 3FFFh is ROM page 0 from the Flash
ROM. It is always present.
The 16K byte address space from 4000h to 7FFFh is used for swapping a 16K byte
ROM page from the Flash ROM. This allows the TI-83 Plus system to extend
beyond its 64K byte physical addressing capabilities.
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