Texas Instruments TI-83-Plus User Manual

44 Chapter 2: TI-83 Plus Specific Information
TI-83 Plus Developer Guide Third Release May 28, 2002
Accessing Archived Variables without Unarchiving
Variable data residing in the archive can be accessed without unarchiving the data to
RAM. This is a read-only operation, an application cannot write data directly to the
archive.
• Locating archived variables
Archived variables will have an entry in the Symbol Table that contains information
on where the data resides in the archive.
The Symbol Table search routines used to locate variables in RAM, FindSym and
ChkFindSym, are also used to locate variables in the archive. See the Accessing
User Variables Stored in RAM section for a detailed explanation of these routines.
If a variable is archived, the output from the Symbol Table search routine will return
two key pieces of information.
B register = ROM page of the start of the archived data.
DE register = the offset on the ROM page to the start of the archived data.
• How is variable data stored in the archive?
The actual data for a variable has the same structure as when it resides in RAM.
See Variable Data Structures section for further information.
In addition to the variable’s data structure, a copy of the variable’s Symbol Table
entry is also stored in the archive. Fig. 2.11 below shows the format used for each
variable stored in the archive.
Data
valid
Size of symbol
entry + Data
Size varies by the name
size and data type
Size computed the same
as variables in RAM
Flag LSB MSB Symbol Table Entry Variable Data Structure
Increasing addresses -------->
Table 2.11: Format of Archive Stored Variables
Archived data for a single variable can cross ROM page boundaries. System
routines to read from the archive are provided to make this cross boundary situation
transparent to applications.
• Reading bytes from the archive
There are two methods provided for reading data from the archive — direct and
cached.
– Direct
This method involves an application reading either one or two bytes at a time
from the archive — supplying both the ROM page and offset to the data to be
read.
Inputs: B register = ROM page of byte(s) to copy

Texas Instruments TI-83-Plus Specifications

General

Brand	Texas Instruments
Model	TI-83-Plus
Category	Calculator
Language	English