TI-82 Link Protocol Guide v1.0 - Silent Variable Transfers

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Silent Variable Transfers

"Silent Linking" is a capability that Texas Instruments built into the TI-83, TI-83+, TI-86, TI-89, TI-92 and TI-92+. It enables the calculator to transfer data to and from a computer without any special preparation required on the calculator end. The only drawback to the silent linking method is that when using this protocol, the calculator will automatically overwrite any data in a variable that has the same name as one being sent to it. Any program that incorporates silent linking must check for this; otherwise data may be lost.

Because silent linking protocols are one-sided (i.e. the user interaction is solely on the computer), there are three different transfer sequences required. First a directory listing must be downloaded from the calculator in order to choose the variables to transfer or to check for duplicate names and out-of-memory conditions. Then, if variables are to be downloaded, a variable request action must be initiated by the computer. Finally, if variables are to be uploaded, a request-to-send action must be sent by the computer.

The TI-82 does not have the directory listing feature, and therefore does not support full silent linking. Nevertheless, the TI-82 implements two silent linking commands for use with the CBL/CBR:

- Variable Request: The TI-82 both sends and responds to this command.
- Request-to-Send: The TI-82 can send this command, but it does not respond to it.

#### Requesting a Variable

The protocol for requesting and receiving a variable from the calculator is shown below.

Step | Direction | Packet
--- | --- | ---
1 |  |  |  | REQ with expected header
2 |  | ACK
3 |  | VAR with actual header
4 |  | ACK
5 |  | CTS or SKIP/EXIT - if exit, quit.
6 |  | ACK
7 |  | DATA
8 |  | ACK

Note: If the requested variable does not exist, step 5 will be the end of the transfer with an EXIT packet.

As with manual transfers, the data section contains the variable data. For information on variable formats, click here.

Example:

PC: | `02 A2 0B 00` `00 00 00 41 00 00 00 00 00 00 00 41 00` | Request Real Number "A"
TI: | `82 56 00 00` | Acknowledgement of request
| `82 06 0B 00` `09 00 00 41 00 00 00 00 00 00 00 4A 00` | Variable Header: Real Number "A"
PC: | `02 56 00 00` | Acknowledgement of variable header
| `02 09 00 00` | Clear to send variable
TI: | `82 56 00 00` | Acknowledgement of CTS
| `82 15 09 00` `00 80 12 56 34 78 85 25 55 93 02` | Variable data: "1.2563478852555"
PC: | `02 56 00 00` | Acknowledgement of variable data

#### Sending a Variable

The protocol for sending a variable from the calculator to a computer or CBL/CBR is shown below.

Step | Direction | Packet
--- | --- | ---
1 |  |  |  | RTS
2 |  | ACK
3 |  | CTS
4 |  | ACK
5 |  | DATA
6 |  | ACK

Again, the data section contains the variable data.

Examples:

TI: | `82 C9 0B 00` `09 00 00 41 00 00 00 00 00 00 00 4A 00` | Request to send Real Number "A"
PC: | `02 56 00 00` | Acknowledgement of request
| `02 09 00 00` | Clear to send variable
TI: | `82 56 00 00` | Acknowledgement of CTS
| `82 15 0A 00` `00 80 12 56 34 78 85 25 55 93 02` | Variable data: "1.2563478852555"
PC: | `02 56 00 00` | Acknowledgement of data

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