Tandy Radio Shack TRS-80 Model 12

Model 12 Model 12 front view

The Model 12 is an further integration if the Model II. The enclosure is white, a bit lower, but has a larger footprint. Where the Model II had four boards for basic operation, the Model 12 had three integrated into a mainboard. The enclosure had room for a 7-slot card cage, but it is not part of the standard machine.

The disk drives in the Model 12 are not running continuously like in the Model II, so this can create problems with using Model II operating systems with the Model 12. The TRSDOS 2.0b was especially modified for this (and using a higher track step rate).

Another feature are the double sided disk drives.

Video/keyboard interface M12 VIDEO KEYBOARD INTERFACE The Model 12 video/keyboard interface board is very similar, but not the same as that of the Model II.
Main board Model 12 main board Three of the the four boards in the model II are part of the main board. Only the Video/keyboard board remains separate. The slot for the Video/keyboard card is in the middle. New is the usage of an FD2793 floppy controller, where the Model II used an FD1791. If a card cage is installed, it uses the card slot and the Video/keyboard card moves to the card cage.

There is only 32 Kbyte on board, so actually it is the complete 3 of the MII 4 four boards. There was an upgrade to 128 kByte on board, however this included exchanging a PROM (see TECHNICAL BULLETINS for the Model 12 & 16b).

Keyboard Model 12 Keyboard
Model 12 Keyboard pcb
The Model 12 uses a capacitive keyboard technique, making is sleeker than the classic Model II keyboard. Also the way of connection changed: the Model II had a cable fixed to the computer and a connector at the keyboard, the Model 12 has the more customary way of a cable fixed to the keyboard and a connector at the computer. Also the wiring changed, but the protocol is the same. So you need a special cable to connect a Model II keyboard to a Model 12 (like when your Model 12 keyboards doesn't work).
Model II keyboard connector / Model 12 computer connector / Name
            1               /            1                / data
            2               /            3                / busy*
            3               /            5                / GND
            4               /            2                / clk
            5               /            4                / +5V
Note that the pin numbering of the DIN connectors is not regular, the pins 4 and 5 were later added between 1,2 and 2,3 respectively (originally for the second stereo channel for audio equipment).

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Last update: 2013-12-15