IBM RT Series Hardware Reference Manual page 316

TNL SN20-9844 (March 1987) to 75X0235
4. The LFG (Logic Function Generator) which performs data conversion functions on the data
stream to and from BAMDA.
5. The video data out logic which transfers the display bit map data image from BAMDA to
the video output connectors and provides video synchronization signals for the monitor.
6. The graphic operation processor which controls all of the adapter functions.
7. The instruction ROM (Read Only Memory) which contains the microcode instructions for
the graphic operation processor.
Command Queue
The command queue is a list of graphic operation commands executed by the graphic operation
processor. The command queue is loaded by the system processor, usually in a linked list. The
processor retrieves these commands and executes them asynchronously from the system.
In its simplest form, the linked list of commands forms a FIFO buffer, with the system loading
commands at one end and the graphic processor executing them at the other end.
Additional features of the command and queue formats allow for branching and interrupting,
thus considerably increasing control flexibility over the simple FIFO approach.
Direct Memory Access (DMA)
The adapter's hardware supports DMA on system DMA channel 7. The DMA graphic
operations are performed during transfers from system memory. Two-dimensional DMA
(TDDMA) cut and paste operations are supported as graphic operations types.
Hardware Cursor
The adapter supports a 48x64 bit hardware cursor which 'AND's and 'XOR's two different
patterns simultaneously to the screen. The cursor patterns are stored in the hidden portion of
the bit map. Memory writes to the appropriate cursor X and Y positioning registers moves the
cursor display position.
4 Extended Monochrome Graphics Adapter