### Green Thumb

The Green Thumb terminal was Tandy's part of Project Green Thumb, an investigation into giving farmers real time access to information useful to their farms. The University of Kentucky led the research with Motorola and Tandy working together on the terminal to be set up in farmer's homes.

The Green Thumb used a TV for display and could talk to the systems through a direct-connect modem. There was a numeric keypad for input with a few special keys to step through downloaded pages. The user would enter their login ID, and item number and sub-item data. The would then dial the number of the server and when connected the Green Thumb would download the pages associated with that item number and sub category.

As such, the Green Thumb emulation does very little without being connected to a server. To demonstrate its operation there is a server program on the Model III utilities diskette. You can run a demonstration with the following command:

`trs80gp -gtdemo`

Note that `-gtdemo` must be the first thing on the command line.

After a moment or two you will see the Model III echo the login and item number as sent by the Green Thumb in packet form. The Green Thumb will show the first page as it downloads. After a good minute or two (or much less if you activate turbo mode on both sides) the Green Thumb will print "READY TO VIEW" at which point you can use the arrow keys to step through the text and graphics pages download from the Model 3. The server always downloads the same pages regardless of the login or item numbers entered.

The built-in demo is equivalent to running:

`trs80gp -m3 -td :tu3 -i "GTDEMO\r" -r [ :gt -icmd [ [ input key ] [ sleep 25 ] [ feed "123*456#98#\r" ] ] ]`

You can also run the demo "by hand" with the following command:

`trs80gp -m3 -td :tu3 -r :gt`

You'll have to start the `GTDEMO` server on the Model III first then type in the `123*456#98#` on the Green Thumb and press Enter. Note that the `*` will show up as a space on screen.

The protocol used by the Green Thumb is packet oriented and somewhat similar to Videotex but very much its own thing. There's no known documentation of it; the demo server was created though reverse engineering of the Green Thumb ROM. Enough is known that it could be documented but this is all there is for now:

- The demo server source code: gtdemo.zip
- A full state diagram
- An abbreviated state diagram
- Disassembled ROM source in trs80gp (Debug → Source Code)

The full state diagram shows how the Green Thumb responds to bytes received from the server including error conditions and invalid bytes. The abbreviated one only shows transitions on expected data bytes, no checksum errors, etc.

On surprise is that unlikely the Videotex and Color Computer the Green Thumb does not use the 6809 microprocessor but instead the more primitive Fairchild F8 (as licensed by Motorola). Nonetheless, trs80gp provides the usual full debugging features for the F8 processor for those so inclined.