HP M2350A Service Manual page 69

Understanding the Computer Module
The Function &rds
Data Transfer
Display data, waves, lines, numerics, display attribute data and control messages are
transferred from the CPC via the MPB to the CDSPCXI'RL. The microprocessor on the
CDSPC-CTRL converts and places this data, via the local bus, into the dual-ported Video RAM
using a Video System Controller on the CDSPC-VIDEO. The display attribute, for example,
half-brightness is 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 RAMS
The Video RAM can be divided into four parts. They are:
Alphanumerics / Graphics plane 1 (1024 x 512 pixels)x 3 color banks)
Alphanumerics / Graphics plane 2 (1024 x 512 pixels)x 3 color banks)
Wave Plane (2048 x 512 pixels)x 3 color banks)
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-, half-brightness and blinking.
The three color banks of the Video RAM -are controlled by the Video Controller chip.
Wave Plane
The wave plane, used for displaying up to 8 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 adding new data onto the right on the screen as old data is displaced on the left.
Color Equalization
The 7 colors produced by the color display have had their intensities
equalized
in such a way
that they appear similar in intensity to the human eye. A resistor network in combination with
some transistors has been used, combining some red and green, to lighten the output of the
blue output on the display. The red output has a slightly higher full intensity voltage to get
brighter alarms.
Summary
n
Displays up to 8 waves, in 7 colors with horizontal scrolling.
n
2 Alphanumeric/graphic planes (1024 x 512 pixels x 3 color banks) for display text, figures
and simple graphics.
n
1 Wave plane with extended resolution (2048 x 512 pixels x 3 color banks) that can display
up to 8 overlapping waves with horizontal scrolling.
n
3 character sizes,
q
Large 32 x 40 pixels
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