Diseño Electrónico: TI83 - TI-83+ Link Protocol Guide v1.0

https://merthsoft.com/linkguide/ti83+/packet.html

TI-83+ Link Protocol Guide v1.0 - Packet formats

Packet Formats

Texas Instruments calculators always send data and responses in self-contained "packets."
Packets have the following format:
Note - all 2-byte integers are transmitted little-endian Intel-style (least significant byte first).

Offset	Length	Description
0	1 byte	Machine ID byte
1	1 byte	Command ID byte
2	2 bytes	Length of data (see note below)
4	n bytes	Data (if attached)
4+n	2 bytes	Checksum (if data is attached)

Note - The "Length of data" element may not be equal to zero if the packet contains no data. In this case, the Command ID byte will indicate that the packet contains no data.

The Machine ID Byte

The Machine ID byte identifies the machine that is sending the packet. It can have one of the following values:

Value	Description
02h	Computer sending TI-82 data
03h	Computer sending TI-83 data
23h	Computer sending TI-83+/TI-84+ data
73h	TI-83+ or TI-84+
82h	TI-82
83h	TI-83

Note: The TI-83 accepts TI-82 and TI-83 Machine ID bytes in order to transfer data between a TI-82/83 and a TI-83+.

The Command ID Byte

The Command ID byte identifies the request or response that the machine is sending. It can have one of the following values:

Value	Description	Data Included
06h	Variable Header (VAR)	A fixed-length, NUL padded variable header
09h	Clear to send (CTS)	None
15h	Data packet (DATA)	Screenshot/variable/backup data
2Dh	Silent - Request Versions (VER)	None
36h	Skip/Exit (SKIP/EXIT)	A five-byte rejection code (see codes below)
56h	Acknowledge (ACK)	None
5Ah	Checksum Error (ERR) The previous packet must be sent again.	None
68h	Check ready (RDY)	None
6Dh	Silent - Request Screenshot (SCR)	None
88h	Silent - Delete Variable (DEL)	A fixed-length, NUL padded variable header
92h	End of Transmission (EOT)	None
A2h	Silent - Request Variable (REQ)	A fixed-length, NUL padded variable header
C9h	Silent - Request to Send Variable (RTS)	A fixed-length, NUL padded variable header

Rejection codes (used with Command ID 36h) can have one of the following values:

Value	Description
01h	EXIT - The entire transmission has been cancelled.
02h	SKIP - The current variable has been skipped.
03h	OUT OF MEMORY (silent transmissions only) - The receiving calculator is out of memory.

The Checksum

The checksum is a 16-bit value used to verify the integrity of the data in the packet. It only present if data is present.
The checksum is calculated by taking the lower 16 bits of the sum of the data bytes, as shown below:

int calculateChecksum(unsigned char* data, unsigned short datalength) {
   unsigned short x, checksum;
   for(x=0; x<datalength; x++) {
      checksum+=data[x];  //overflow automatically limits to 16 bits
   }
   return checksum;
}

Variable Headers

A Variable header contains information about one variable in the calculator.

Offset	Length	Description
0	2 bytes	Size of actual variable data, in bytes
2	1 byte	Type ID Byte (see type ID's below)
3	8 bytes	Variable name, padded on the right with NULL characters (0h). This field is always tokenized. Not used for ID list.
11	1 byte	Version - Always has a value of 0h.
12	1 byte	Type ID Byte 2 - Always has a value of 0h. Note: bit 7 is set if archived. Not used for getting certificates.

Note: These bytes only make up the "data" section of the packet.
Note2:
- for lists (L1..L6), the first token is a 5D byte followed by another byte: 00 for L1 to 05 for L6.
- for equations: there are 31 equations (Y1..Y0 in func mode, X1t..X6t and Y1t..Y6t in param mode, r1..r6 in polar mode and FnOn/FnOff in On/Off mode). The varname is 5E10 for Y1 to 5E19 for Y0. The varname is 5E20 for X1t, 5E21 for Y1t to 5E2A for X6t, 5E2B for Y6t. The varname is 5E40 for r1 to 5E45 for r6. The varname is 5E80 for u to 5E82 for w.
- for strings: there are 10 strings (Str1..Str9). The varname is AA00 for Str1 to AA09 for Str0.
- for pictures: there are 10 pictures (Pic1..Pic0). The varname is 6000 for Pic1 to 6009 for Pic0.
- for gdbs: there are 10 gdbs (GDB1..GDB0). The varname is 6100 for GDB1 to 6109 for GDB9.

The Type ID Byte

The type ID byte specifies the type of variable that is being transmitted. It can have one of the following values:

Value	Description (click for variable format)
00h	Real Number
01h	Real List
02h	Matrix
03h	Y-Variable
04h	String
05h	Program
06h	Edit-locked Program
07h	Picture
08h	GDB
0Bh	Window Settings (See note below)
0Ch	Complex Number
0Dh	Complex List
0Fh	Window Settings (See note below)
10h	Saved Window Settings (See note below)
11h	Table Setup (See note below)
13h	Backup
14h	Used to delete a FLASH application
15h	Application Variable
17h	Group Variable (only found on TI83+)
19h	Directory (See note below) - only used when requesting a directory
23h	FLASH Operating System
24h	FLASH Application
26h	ID list
27h	Get Certificate
29h	Clock

Note - If the Type ID is in the range 0Fh - 12h or 19h, then the contents of the name field of the header do not matter.

Backup Header Format

If the type ID byte specifies a backup, the variable header takes the following 9-byte format :

Offset	Length	Description
0	2 bytes	Size of first backup section (flags area), in bytes
2	1 byte	Type ID Byte (13h in this case)
3	2 bytes	Size of second backup section (data area), in bytes
5	2 bytes	Size of third backup section (symbol area), in bytes
7	2 bytes	Start User Area Address

FLASH Header Format

If the type ID byte is in the range 22...28h, the variable header takes the following 10-byte format :

Offset	Length	Description
0	2 bytes	Size of actual data, in bytes (LSB).
2	1 byte	Type ID Byte (see type ID's below)
3	2 bytes	Size of actual data, in bytes (MSB). Usually 128/256 bytes.
5	1 byte	Flag - Always has a value of 0h but bit 7 is set if archived (*).
6	2 bytes	FLASH offset
8	2 bytes	FLASH page