TI-92 Link Protocol Guide - Screenshots

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Screenshots

The TI-92's screenshot ability is "silent," which means that the calculator does not need to be put in a special mode. Screenshots can be taken any time the calculator is ready to accept a keypress.

The protocol used for getting a screenshot is shown below. For information on packet formats, click here.

Step | Direction | Packet
--- | --- | ---
1 |  |  |  | SCR
2 |  | ACK
3 |  | DATA - Format described below.
4 |  | ACK

The data packet contains a 3840-byte monochrome bitmap (1 bit per pixel). Each bit has a value of 1 if the corresponding pixel is dark or a value of 0 if the corresponding pixel is light.

The pixel order is left-to-right, then top-to-bottom (See figure below).
Byte 0 defines the first 8 pixels in the left side of the top row of the screen. Bytes 1-29 define the rest of the first row, bytes 30-59 define the second row, etc.

Example:

PC: | `09 6D 00 00` | Screenshot request
TI: | `89 56 00 00` | Acknowledgement of request
| `89 15 00 0F` <3840 bytes plus 2 byte checksum> | Screen data
PC: | `09 56 00 00` | Acknowledgement of data

The following figure demonstrates byte ordering of the pixels if the bitmap is in a 3840-element array data[]:

Note that this format is different from the standard Windows bitmap format, which specifies a value of 1 if the pixel is light and bottom-to-top row order.

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