Connection; Data Transfer; Videoram; Wave Plane - HP M2350A Service Manual

Understanding the Computer Module
The Function Cards
All display data, including local language characters, are produced by the CPU and transferred
via the MPB.
Note
The Japanese character set is too large to be dealt with on the CPU, so these
characters are stored on a local EPROM card which is placed in the same
cluster as the display controller.
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The DSPC only controls the mechanism of actually displaying information on the screen.
Connection
The DSPC card must be inserted into the rear of the computer module so it can be connected
to the display. The integral monochrome display is connected via a g-pin D-type connector on
the card's edge to a similar connector on the rear of the display.
Data Transfer
Display data, waves, lines, numerics, display attribute data and control messages are
transferred from the CPU via the MPB to the DSPC. The microprocessor on the DSPC converts
and places this data into the dual-ported Video RAM using a Video System Controller. The
display attributes (for example, half-brightness) are also placed in the Video RAM.
The pixel data is clocked out of the Video RAM by the on-chip shift registers. This data then
passes through the SLIP Chip which contains all the video and addressing logic before passing
it to the video buffers. The data then passes through the protection network for output to the
display, using an oscillator to synchronize the picture sweep.
Video RAM
The video RAM can be divided into four parts. They are:
Alphanumerics / Graphics plane 1
(1024 x 512 pixels)
Alphanumerics / Graphics plane 2 (1024 x 512 pixels)
Wave Plane (2948 x 512 pixels)
Attribute Map
( 256 x 256
bytes )
The two alphanumeric / graphics planes are used to display text, figures and basic graphics
(lines, boxes etc). The higher resolution wave plane is used for displaying the parameter
waves, for example, ECG. (See following paragraph.) The attribute map is used to enable parts
of the screen and select between full-brightness, half-brightness and blinking.
Wave Plane
The wave plane, used for displaying up to 6 overlapping parameter waves, is implemented in
a different way than for the other planes. The reason for this is the wave plane must display
waves that scroll horizontally on the monitor. The scrolling logic moves a pointer, indicating the
left of the screen, through the video RAM and new data is written directly behind it. This has
the result of moving the trace by adding new data onto the right of the screen as old data is
displaced on the left.
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