ViewSonic VG181 Service Manual page 20

Service Manual ViewSonic
VG181 July 2000 - Version 1.0
THEORY OF CIRCUIT OPERATION
The sync decoder detects and processes the horizontal sync (GHS), vertical syne
(GVS) , sync on green (GSOG) , and field (GFIELD) inputs used for timing. There
are several bits to indicate the status of the inputs. For horizontal sync, HSOK=1
indicates that the horizontal
line rate is faster than
10KHz.
For vertical sync,
VSOK=1 indicates that the vertical field or frame rate is faster than 10Hz. For sync
on green, SOGACT=1 indicates that transitions on GSOG are occurring faster than
10Hz.
Output GHSFOUT is the field output signal used to tell an external ADC whether
even or odd pixels are being captured during half sample mode.
When EXTFCE=1 the external flow control is enabled, each new line is marked by
an edge on the GLAVIN input (pin GFBK), but while EXTFCE=0 the GFBKINinput
(pin GFBK) is used as the input HSYNC signal for pixel counters.
Display port
The block diagram of display port is as follows :
Scaled
Display
Data
DRE[7: 0}
DGE[7:0}
DBE[7:0]
on
Screen
Display
Overlay
Ate DRO[7: 0}
ata
DGOI7:0}
DBO[7:0}
Display
Timing
Generator
DCKEXT
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