(c)
The Input/Output processor circuits contain a microprocessor. The circuits perform the following functions: 1) Provide and control six independent direct memory access
(DMA) channels, used for communicating with various sections of the symbol generator. 2) Determine which inputs on the analog input/output circuits will be processed.
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3) Receive input data from analog input/output circuits, process the input data, and store the data in the memory (RAM).
4) Store in memory (RAM), interpreted display tables used by the graphics section.
(4) Display Generation
(a)
At the completion of processing, the display tables provide all the data required for video generation on the EADIs and the EHSIs. The displays on the EADIs and EHSIs are drawn as vectors, arcs, characters and special symbols in seven colors of two intensities. The presentation contains dynamic displays overlaying a background of fixed displays. For example, a glide slope pointer moving up and down a fixed scale.
(b)
Two different techniques are used to display the data on the EADIs and EHSIs. These techniques are stroke and raster. The special symbols, characters, letters, vectors and arcs are displayed using the stroke method. The EADI sky/ground ball or EHSI weather radar data are displayed using the raster method. The symbol generator has two raster channels, one for the EHSI and one for the EADI. The symbol generator has only one stroke channel, which is time-shared between the EADI and EHSI. When the raster data is being written on the EHSI, the stroke channel services the EADI, and vice versa. The raster and stroke control is sent from the symbol generator to the display units.
(c)
The display tables stored in the memory of the input/output processor circuits are read out by the graphics section. The display tables contain stroke directives (stroke data and instructions), and raster directives (raster data and instructions).
(d)
The circuits that make up the symbol generator graphics section are display driver circuits, stroke generation circuits, EADI raster generation circuits, and EHSI raster generation circuits. The graphics section uses the display table instuctions, stored in the memory of the Input/Output processor circuitry, and translates the data into analog deflection and video signals. The graphics section sends the deflection and video signals to the display units, while maintaining a refresh rate high enough to avoid observable flicker.
(e)
During the stroke mode, the stroke directives are sent to the stroke generation circuitry. The stroke generation circuitry provides the following major functions: 1) Beam Positioning 2) Generation of straight and curved vectors 3) Generation of predetermined symbols and characters 4) Selection of video and color
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