TI-86 Link Protocol Guide v1.0 - File formats

The TI-86 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 ".86g". However, all of these file types have a common format.

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

Extension	Description
.86c	TI-86 complex number
.86d	TI-86 GDB (function, polar, parametric or differential equation)
.86e	TI-86 equation
.86g	Multiple TI-86 variables of varying types (group)
.86i	TI-86 picture (image)
.86k	TI-86 constant (real or complex)
.86l	TI-86 list (real or complex)
.86m	TI-86 matrix (real or complex)
.86n	TI-86 real number
.86p	TI-86 program
.86s	TI-86 string
.86v	TI-86 vector
.86w	TI-86 window settings (Func, Pol, Param, DifEq or ZSTO)

The TI-86 variable file format

The TI-86 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 "**TI86**".
8	3 bytes	3-byte further signature. These three bytes always contain {1Ah, 0Ah, 00h} = {26, 10, 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	Always has a value of 12 (Ch).
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	8 bytes	Variable name, padded with space characters (0x20) on the right. (*)
14 (Eh)	2 bytes	Length, in bytes, of the variable data. (This is a copy of the value in offset 2)
16 (10h)	n bytes	Variable data. Click here for variable data formats.

(*) Note of Adrian Mettler (TiLP bug #837114) :

There are in fact at least THREE conventions for storing variable names in TI-86 files in the wild, and affect all
variable types. These are the "official" one generated by the current version of TI's software (and documented in the
references that I've seen online), a slight modification of this format, and the third one, closer to the wire format, 
that is created by some third-party programs (and perhaps by old versions of TI's own software and by TI85). All three are 
correctly read by TI's software without complaint.  

The difference between the three versions is that TI's official version (1) always includes padding of the name
field up to 8 characters, using spaces ('\20') for the extra characters.  A common variant (2), currently written by
TiLP, uses null characters ('\0') to pad up to eight characters.  The third variant (3) DOES NOT pad at all (aka TI-85 format). 
The fourth variant (4) always contains 8 chars but with garbage (eg 03  BE 61 69 70 31 20 20 20).

The current release of TiLP correctly reads files that follow conventions (1) and (2), and gets really confused on
files of type (3) and (4). 

A Proprietary TI-86 backup file format

Even if the TI-86 Graph Link software does not support system backups for TI85/86 calculators, this functionnality is implemented in the calculator OS. In this way, it's possible to download and save system backups with the extension ".86b".

This is the reason why FastLink and TiLP have their own file format.

FastLink uses this file format for TI-86 backups:

Offset	Length	Description
0	8 bytes	8-character signature. The signature is always "**TI86**".
8	3 bytes	3-byte further signature. These three bytes always contain {1Ah, 0Ah, 00h} = {26, 10, 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 first data section. This number should be 16 (10h) bytes more than the length of the first data section as reported in the backup header.
55 (37h)	16 bytes	The backup header (format described below).
71 (47h)	x bytes	First data section.
71 (47h)+x	2 bytes	First checksum. This is the lower 16 bits of the sum of all bytes in the backup header and the first data section.
73 (49h)+x	2 bytes	Length, in bytes, of the second data section
75 (4Bh)+x	y bytes	Second data section.
75 (4Bh)+x+y	2 bytes	Second checksum. This is the lower 16 bits of the sum of all bytes in the second data section.
77 (4Dh)+x+y	2 bytes	Length, in bytes, of the third data section
79 (4Fh)+x+y	z bytes	Third data section
79 (4Fh)+x+y+z	2 bytes	Third checksum. This is the lower 16 bits of the sum of all bytes in the third data section, or 0 if the third data section is empty (has length 0).
81 (51h)+x+y+z	2 bytes	Length, in bytes of the fourth data section
83 (53h)+x+y+z	w bytes	Fourth data section.
83 (53h)+x+y+z+w	2 bytes	Fourth checksum. This is the lower 16 bits of the sum of all bytes in the fourth data section.

The Backup Header has the following format:

Offset	Length	Description
0	2 bytes	Offset to data length: Always has a value of Ch (12).
2	2 bytes	Length, in bytes, of the first data section.
4	1 byte	Type ID: Always has a value of 1Dh.
5	1 byte	Length, in characters, of the name: Always has a value of 6.
6	8 bytes	Name: "SYSTEM" padded with space characters (20h) on the right.
14 (Eh)	2 bytes	Length, in bytes, of the first data section.

TiLP uses this file format for TI-86 backups:

This format is based on a TI85 backup format which has been extended for adding a fourth section.

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 15 (Fh).
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
11	2 bytes	Length, in bytes, of the fourth data section.