Page 337 - Understanding Automotive Electronics

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9 AUTOMOTIVE INSTRUMENTATION

Figure 9.25
Video Signal
Generation

FPO

internal record of the current active line on the CRT by counting vertical
sync pulses. The actual bit pattern associated with the character being
displayed along the active line on the CRT is loaded into the shift register.
This data comes in eight separated 8-bit bytes from video RAM. Then during
the scanning of the active line, the bit pattern is shifted out one bit at a time
by a pulse signal, H , at a frequency that is 256 times that of the horizontal
ck
sync frequency.
Each bit location in the shift register corresponds to a pixel location on
the CRT screen. A “1” stored at any shift register location corresponds to a
bright spot on the CRT. Thus, by placing a suitable pattern in the shift register
for a particular line, it is possible to display complex alphanumeric or pictorial
data on the CRT.
The enormous flexibility of the CRT display offers the potential for a very
sophisticated automotive instrumentation system. In addition to displaying the

324 UNDERSTANDING AUTOMOTIVE ELECTRONICS