Overview

The Terebi Oekaki (テレビおえかき) was released in Japan in 1985. It consists of a drawing software cartridge connected to a custom graphic board. The board detects positioning on a transparent surface. A Sega-labelled plastic pen is provided in the package, but another item can be used.

Relying on cheap 1985 home-technology, position detection is imprecise and using the actual board is known to be tedious.

The graphic software is compatible with Sega SG-1000, SC-3000 and Master System. It relies on legacy video mode 2, which is not supported by the Mega Drive VDP. Limitations of video mode 2 mean that graphic artefacts are often shown when trying to draw using more than 2 colors in a given tile.

How it works

The dedicated cartridge intercepts reads and writes to special memory mapped registers, in order to let the software communicate with the board.

AddressAccessBits
  76543210
$6000W-------AXIS
$8000RBUSY------PRESS
$A000R/WDATA
AXIS
write 0 to select X axis, 1 to select Y axis.
BUSY
reads 1 when graphic board is busy sampling position, else 0.
PRESS
reads 0 when pen is touching graphic board, else 1.
DATA
when pen is touching graphic board, return 8-bit sample position for currently selected axis (X is in the 0-255 range, Y in the 0-191 range). Else, return 0.

It's interesting to note that most items, including the provided plastic pen, are too big to allow touching the extreme positions. In most cases, about 4-5 pixels may be inaccessible on each side of each dimension.

Addresses listed above are standard addresses as used by the Terebi Oekaki graphic software. It is likely (but unverified) that hardware addressing on the cartridge allows access to the registers from a whole 8 Kilobyte range (eg: AXIS bit might be accessible on the whole $6000-7FFF range).

Links

There's very little information about the Terebi Oekaki on the internet. Our (outdated) software release page has some of them: Terebi Oekaki


Researched by Bock




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