5-1
SECTION VMODE DISCRIMINATION CIRCUIT AND SYNC
SIGNAL PROCESSING CIRCUIT
Mode discriminating circuit performs to discriminate the kind of signals ; the signal which is input to D-SUB connector, is VGA,
or is Macintosh signal.
Sync signal processing circuit performs to process sync signals into shape which can be utilized in horizontal and vertical osc
circuits, because the signals which are input to D-SUB connector from a personal computer have various figures.
1.OUTLINE OF MODE DISCRIMINATING CIRCUIT
This model, for the simplification, reduces discriminating functions than CRT monitor for computer. The functions are those:
to identify VGA signal or not; horizontal scanning frequency is higher or lower than 28kHz; the signal is input or not.
NO SIGNAL
DISCRIMINATION
ICH01, QH06
POLARITY
DISCRIMINATION
ICH01
FREQUENCY
DISCRIMINATION
ICH04, ICH05
DECODER
ICH02
No signal
VGA480
VGA400
VGA350
Hor. sync
Vert. sync
Low frequency
Fig. 1
VGA has three modes by number of vertical line. These are made to be able identify by polarity of horizontal and vertical sync
signal. The difference of VGA mode signal is described in Table-1.
Kind No. of Ver. line fH fV Hor. Sync polarity Ver. Sync polarity
VGA480 480 31.5kHz 60Hz Negative Negative
VGA400 400 31.5kHz 70Hz Negative Positive
VGA350 350 31.5kHz 70Hz Positive Negative
Table-1
The above discriminated output is supplied to Ch. selection IC ICA01, and to be used as a sign to switch operations of related
circuit.
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