'*****************************************************************************
'*
'* Some details about the construction of the LCD of a Tandy Model 100:
'*
'* The display consists of 10 sections, called "drivers" throughout
'* this code. Each "driver" is associated with a memory of 64 * 4 bytes,
'* with pixels arranged in this way:
'*
'*  offs  +0  +1  +2  +3  +4  +5    +48 +49
'* base +---+---+---+---+---+---...+---+---+
'* 0    | 0 | 0 |   |   |   |      |   | 0 | 
'*      +---+---+---+---+---+---   +---+---+
'*      | 1 | 1 |   |   |   |      |   | 1 | 
'*      +---+---+---+---+---+---   +---+---+
'*           ...                      ...
'*      | 7 | 7 |   |   |   |      |   | 7 | 
'*      +===+===+===+===+===+===   +===+===+
'* 64   | 0 | 0 |   |   |   |      |   | 0 | 
'*      +---+---+---+---+---+---   +---+---+
'*      | 1 | 1 |   |   |   |      |   | 1 | 
'*      +---+---+---+---+---+---   +---+---+
'*           ...                      ...
'*      | 7 | 7 |   |   |   |      |   |  7| 
'*      +===+===+===+===+===+===   +===+===+
'* 128  | 0 | 0 |   |   |   |      |   | 0 | 
'*      +---+---+---+---+---+---   +---+---+
'*      | 1 | 1 |   |   |   |      |   | 1 | 
'*      +---+---+---+---+---+---   +---+---+
'*           ...                      ...
'*      | 7 | 7 |   |   |   |      |   |  7| 
'*      +===+===+===+===+===+===   +===+===+
'* 192  | 0 | 0 |   |   |   |      |   | 0 | 
'*      +---+---+---+---+---+---   +---+---+
'*      | 1 | 1 |   |   |   |      |   | 1 | 
'*      +---+---+---+---+---+---   +---+---+
'*           ...                      ...
'*      | 7 | 7 |   |   |   |      |   | 7 | 
'*      +===+===+===+===+===+===...+===+===+
'*
'* NB: columns 50-63 have no dots on the display (but memory cells?)
'*
'* So each of the "drivers" is a 50x32 pixel panel, with 4 rows of
'* 8 pixels height each. They are addressed at offsets 0, 64, 128,
'* and 192 respectively; the colum (X coordinate) is the offset.
'* Bit 0 of each LCD memory cell is the topmost pixel in a "driver" row.
'*
'* The layout of the 10 "drivers" across the entire display is this:
'*
'*    X 0  -   49 50  -  99 100 - 149 150 - 199 200 - 249
'*  Y  +---------+---------+---------+---------+---------+
'* 0   |         |         |         |         |         |
'* |   |  drv0   |  drv1   |  drv2   |  drv3   |  drv4   |
'* 31  |         |         |         |         |         |
'*     +---------+---------+---------+---------+---------+
'* 32  |         |         |         |         |         |
'* |   |  drv5   |  drv6   |  drv7   |  drv8   |  drv9   |
'* 63  |         |         |         |         |         |
'*     +---------+---------+---------+---------+---------+
'*
'* The ROM uses a 6x8 character generator, which gives a character
'* cell resolution of 41 2/3 by 8 (colums * rows). It is really
'* 40 x 8, (240 x 64 pixels), because the rightmost 10 pixels are
'* not used at all (as far as I know).
'*
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