Hardware Layer; Z80 Cpu And Memory; Fig. 2.3: Z80 Memory Space - Texas Instruments TI-83 Plus Manual

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H L
ARDWARE
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.
0000h
16K Always Flash ROM Page 0
4000h
16K RAM Page 0,1 or Flash ROM Pages 0-31
8000h
16K RAM Page 0,1 or Flash ROM Pages 0-31
C000h
16K Always RAM Page 0
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.
TI-83 Plus Developer Guide
AYER

Fig. 2.3: Z80 Memory Space

Chapter 2: TI-83 Plus Specific Information
3FFFh
7FFFh
BFFFh
FFFFh
Third Release May 28, 2002