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TNL SN20-9844 (March 1987) to 75X0235
Programming Interface
This section describes the programming interface and the key architectural features of the
Extended Monochrome Graphics Display Adapter.
Memory Map
The adapter provides the system processor with direct access to a 1M-pel bit map. A portion of
this bit map is logically dual-ported to the monitor as a video frame buffer.
Bit Addressability
Hardware assist allows the system to address down to the bit level. Bit mask logic allows
selective writing of from 1 to 16 bits automatically. Logical functions such as 'AND', 'OR' or
'XOR' are also specified during the writing of selected bits. Bit alignment, masking and rotation
(barrel shifting) are all performed by hardware within the adapter, thus freeing the system
processor and increasing I/O channel availability.
Orthogonal Access
A unique memory organization and support logic, called Bit Addressable Multidimensional
Array (BAMBA), implements the X, Y bit map. BAMBA supports a mode which directly
addresses 1 to 16 bits in the vertical and the conventional horizontal direction. The vertical
mode also supports bit addressability. All masking and rotation are performed by hardware, thus
allowing high speed graphic operations.
Extended Monochrome Graphics Adapter 5
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