Page 336 - Understanding Automotive Electronics

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AUTOMOTIVE INSTRUMENTATION 9

The operation of the CRT controller is under control of the
instrumentation computer. This computer transfers data that is to be
displayed to the video RAM, and signals the CRT controller via the UART
link. During the display time, the MPU operates under control of programs
stored in the DROM. These programs cause the MPU to transfer data from
the video RAM to the video IC (chip) in the correct sequence for display.
The details of the transfer of data to the video IC and the corresponding
generation of video signals vary from system to system. In the hypothetical
system seen in Figure 9.22, the display on the CRT screen consists of a
sequence of data arranged in 256 rows vertically by 256 horizontally. Here the
display generates the characters F and P (see Figure 9.24). The dots are
generated by switching on the electron beam at the desired location. The beam
is switched by pulsing the video voltage at the time relative to H and V at
s
s
which a dot is to appear. The resolution of the display is one dot, which is often
termed a pixel (picture element).
A typical CRT uses a ras- A scheme for generating the suitable video signals for such a display is
ter scan method and shown (greatly simplified) in the block diagram of Figure 9.25. During the
generates dots on the horizontal retrace time when the electron beam is moving rapidly from right
screen by means of suit- to left, the MPU (under program control) determines which data pattern is
ably timed video signals. to be displayed during the next scanning line. The MPU maintains an

Figure 9.24
Display of FPO
Characters F and P

UNDERSTANDING AUTOMOTIVE ELECTRONICS 323