ELSA ERAZOR III LT, User Manual

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All about graphics
ELSA ERAZOR III Pro and ELSA ERAZOR III LT
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DDC2B
A bi-directional data channel based on the I2C access-bus protocol is used for the com-
munication between monitor and graphics board. In the case of a standard IBM VGA
compatible 15-pin monitor connector, pin 12 (formerly used as monitor ID bit 1) is used
for data transmission (SDA), and the pin 15 (formerly used as monitor ID bit 3) is used as
transmission clock (SCL). The graphics board can request the short EDID information (see
DDC1) as well as the more comprehensive VDIF information (VESA Display Identification
File).
DDC2AB
With DDC2AB additional to DDC2B, the computer can send commands for controlling the
monitor, e.g. for adjusting the screen position or the brightness (similar to ACCESS bus).
Modern monitors and graphics boards no longer use this standard.
The pin assignment of the VGA D-shell socket can be found in the chapter 'Technical
data'.
Video signal formats
There are two common standards for the transmission of video signals: Composite video
and S video. The IEEE 1394 format is currently supported only by Sony equipment.
The monitor and graphics board communicate on three color channels. The color infor-
mation is split into three color signals for red, green and blue (RGB). Video information
for a television, on the other hand, only makes a distinction between monochrome and
color information (luminance and chrominance).
Composite video
Composite video––also known as FBAS––packs the luminance and chrominance infor-
mation in a single signal. In this way, all the information required for a video image can
be transmitted over a single cable. This method is a great benefit for transmissions from
a television transmitter. But this method also has clear disadvantages regarding signal
quality: The nesting of luminescence (Y) and chrominance (C) is imprecise and leads to
errors in the video image.
S-VHS
The solution to the disadvantages of composite video format is clear. S-VHS or Y/C
offers the answer: the separation of the Y and C signals. The cost of having the second
cable necessary to implement this is more than compensated for by the enhanced image
quality. Video cameras that use the Hi-8 or SVHS-C method separate the Y and the C