TI-85 Link Protocol Guide v1.0 - File formats

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File Formats

The TI-85 Graph Link software stores variables in several types of files. Single variables are stored in files that have an extension that corresponds with their type. Groups of variables are stored in files with the extension ".85g". However, all of these file types have a common format (excepting backups).

The different file types and contents that the TI-86 Graph Link software can read and write are shown below.

Extension | Description
--- | ---
.85b | TI-85 system backup
.85c | TI-85 complex number
.85d | TI-85 GDB (function, polar, parametric or differential equation)
.85e | TI-85 equation
.85g | Multiple TI-85 variables of varying types (group)
.85i | TI-85 picture (image)
.85k | TI-85 constant (real or complex)
.85l | TI-85 list (real or complex)
.85m | TI-85 matrix (real or complex)
.85n | TI-85 real number
.85p | TI-85 program
.85r | TI-85 range (Func, Pol, Param, DifEq or ZSTO)
.85s | TI-85 string
.85v | TI-85 vector

### The TI-85 variable file format

The TI-85 variable file format has two parts: a header and several variable entries.

The header appears at the beginning of the file and takes the following format:
Note - All 2-byte integers are stored little-endian Intel-style (least significant byte first).

Offset | Length | Description
--- | --- | ---
0 | 8 bytes | 8-character signature. The signature is always "`**TI85**`".
8 | 3 bytes | 3-byte further signature. These three bytes always contain {1Ah, 0Ch, 00h} = {26, 12, 0}
11 (Bh) | 42 (2Ah) bytes | Comment. The comment is either zero-terminated or padded on the right with space characters.
53 (35h) | 2 bytes | Length, in bytes, of the data section of the file. This number should be 57 (39h) bytes less than the file size.
55 (37h) | n bytes | Data section - consists of a number of variable entries (described below).
55 (37h)+n | 2 bytes | File checksum. This is the lower 16 bits of the sum of all bytes in the data section.

Each variable entry follows this format:

Offset | Length | Description
--- | --- | ---
0 | 2 bytes | Offset to data length: 6 plus the length, in characters, of the variable name.
2 | 2 bytes | Length, in bytes, of the variable data.
4 | 1 byte | variable type ID byte (see variable type ID's)
5 | 1 byte | Length, in characters, of the variable name
6 | m bytes | Variable name (not zero-terminated).
6+m | 2 bytes | Length, in bytes, of the variable data (This is a copy of the value in offset 2).
8+m | n bytes | Variable data. Click here for variable data formats.

### The TI-85 backup file format

Most link programs allow a user to download and save system backups with the extension ".85b".

Here is the format for backup files:

Offset | Length | Description
--- | --- | ---
0 | 8 bytes | 8-character signature. The signature is always "`**TI85**`".
8 | 3 bytes | 3-byte further signature. These three bytes always contain {1Ah, 0Ch, 00h} = {26, 12, 0}
11 (Bh) | 42 (2Ah) bytes | Comment. The comment is either zero-terminated or padded on the right with space characters.
53 (35h) | 2 bytes | Length, in bytes, of the backup header and the data sections. This number should be 17 (11h) bytes more than the sum of the lengths of the three data sections as reported in the backup header.
55 (37h) | 11 bytes | The backup header (format described below).
66 (42h) | 2 bytes | Length, in bytes, of the firstdata section
68 (44h) | x bytes | First data section.
68 (44h)+x | 2 bytes | Length, in bytes, of the second data section
70 (46h)+x | y bytes | Second data section.
70 (46h)+x+y | 2 bytes | Length, in bytes, of the third data section
72 (48h)+x+y | z bytes | Third data section
72 (48h)+x+y+z | 2 bytes | Checksum. This is the lower 16 bits of the sum of all bytes in the backup header and data sections.

The backup header has this format:

Offset | Length | Description
--- | --- | ---
0 | 2 bytes | Offset to data length: Always has a value of 9.
2 | 2 bytes | Length, in bytes, of the first data section.
4 | 1 byte | Type ID: Always has a value of 1Dh.
5 | 2 bytes | Length, in bytes, of the second data section.
7 | 2 bytes | Length, in bytes, of the third data section.
9 | 2 bytes | Memory address of the second data section

Variable Formats | Table of Contents | Tokens and Characters

Site maintained by Romain Liévin (roms@lpg.ticalc.org) and Tim Singer (tsinger@gladstone.uoregon.edu)