Service manual

30 Chapter 4: System Overview
Back End Overview
The Back End subsystem is responsible for the conversion of raw acquisition data into a raster image ready for
display. The Back End subsystem also contains the video data path that supports generation of video comprising
of the ultrasound image as well as graphics annotation. Video generation of both standard composite interlaced
video and progressive scan video is supported. Most functionality is within the ASIC but the memory resources for
acquisition memory, and display memory are found in external memory components. The conversion from PC
type video to TV type video is also performed externally.
Control is received initially from the CPU to setup each functional block and afterward the hardware is completely
data driven. This control takes the form of programming setup registers inside the blocks and setting up scan
conversion tables. Each block provides temporary storage as required to buffer data and keep their respective
processing pipeline full and operating. Also note that the block diagrams show only the data path, but each block
is responsible for generating any necessary memory addresses for their respective input data stream.
The Edge Back End subsystem is shown in the figure below.
Figure 4.5 Back End Subsystem Block Diagram
The Back End Subsystem performs processing encompassing three main data domains, acquisition data, raster
data, and video data. Support for acquisition data includes the input buffer, flash suppression, frame average, and
external ACQ memory. Cine buffer management is performed by the acquisition controller. Conversion from
acquisition data to raster data is performed by the graphics overlay, scan conversion engine, sweeping engine,
and 3D engine. Raster data is stored in an external DISPLAY memory. Also supporting raster operations is the
graphics support block that provides acceleration hardware for pixel operations from the CPU and graphics over-
lay engine. Video data is processed as progressive scan and supplied externally on a digital bus. In addition, inter-
laced video is supplied in both composite and S-video formats. The progressive video path includes buffers,
priority logic, and LUTs. External video in signals are input and multiplexed onto the external video out path to
allow for external sources to display information on connected displays, VCRs, or printers.