Theory of Operation
3–12
TDS 340A, TDS 360 & TDS 380 Technical Reference
The NVRAM (U605) consists of a single nonvolatile memory IC. This RAM
provides long-term power-off storage of front-panel settings, waveforms, and
calibration constants.
Dynamic RAM U704 is organized as 256 K 16 for a total of 512 kbytes. It is
controlled by the ADG250 display controller (U701).
During a normal 68331 access the ADG250 multiplexes the address (on A2 to
A19) onto the A0 to A8 address lines and creates control signals ~RAS, ~CAS,
~XWL, ~XWU, and ~XOE.
A display controller IC processes text and waveforms. The display system sends
the text and waveform information to the monitor assembly as a video signal.
The display system also generates vertical (VSYNC) and horizontal (HSYNC)
sync signals for the monitor assembly.
The display circuit’s primary function is writing waveforms into waveform
planes. The circuitry provides Vector, Dot, Vector Accumulate, Dot Accumulate,
XY, and YT display modes.
The display system provides text, graticule, and waveform bit planes. All
information displayed is first written to a plane. Planes are stored in dedicated
DRAMS along with the vector lists. The information is sent at regular refresh
intervals as an analog video signal.
The waveform display circuit takes a list of sample points, translates them into
intensities for the bit map, writes those intensities to the bit map in the proper
location, and interrupts the CPU when it is done.
— Four vector lists available from U706 store waveform sample
data. Before starting a normal display mode, the CPU writes data to a vector list.
Rasterizers. The display controller (U701) provides two rasterizers. Their
primary function is to “draw” vectors between sample points. The display
controller also performs the top and bottom clip display functions on waveforms.
Video Timing. Q701–Q704 and associated circuitry convert digital video signals
from the display controller into an analog video signal, with two levels con-
trolled by VIDEO LEVEL and INTENS LEVEL from the daculator. The display
controller also creates monitor timing HSYNC (31.25 Hz) and VSYNC (60 Hz).
U703D, U708D, and U709 generate AUX HSYNC, AUX VSYNC and AUX
VIDEO for the Option 14 VGA Video output connector.
Display System
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