SDA9361 Datasheet, PDF (25/47 Pages) Siemens Semiconductor Group – DDC-PLUS-Deflection Controller

SDA 9361
Vertical Scan (width0 and width1)
The total width of this control item is 10 Bit. Therefore two registers (width0 and width1)
are necessary. If enabled (STE = 1) it defines the duration of the vertical scan. When the
vertical period has more lines than the sum of Start Vertical Scan and Vertical Scan,
the calculation of the vertical saw-tooth, the east/west parabola and the vertical parabola
required for HD stops so that the corresponding output signals remain unchanged till the
next vertical synchron pulse.
Guard Band
This control item is useful for optimizing self adaptation. Video signals with different
number of lines in consecutive fields (e. g. VCR search mode) must not start the
procedure of self adaptation. But switching between different TV standards has to
change the slope of the vertical saw-tooth getting always the same amplitude (self
adaptation). To avoid problems with flicker free TV systems which have alternating
number of lines per field an average value of four consecutive fields is calculated. If the
deviation of these average values (e.g. PAL: 312.5 lines or 625 half lines) is less or
equals Guard Band, no adaptation takes place. When it exceeds Guard Band, the
vertical slope will be changed.
Start Reduced Scan
If enabled (SRSE = 1) this item defines the start of the D/A conversion of the calculated
vertical saw-tooth. From begin of the vertical flyback to the line defined by Start
Reduced Scan the output signals VD+, VD- remain unchanged (flyback level). Other
outputs are not affected.
a) control bits VR1, VR0 # 00 (reduction of vertical size)
In this case the byte is useful for e.g. displaying 16/9 source format on 4/3 picture
tubes without visible RGB lines generated of the automatic cut-off control (partial
overscan). It defines the start of the reduced amplitude (factors 0.5, 0.66, 0.75) of the
vertical saw-tooth (refer page 39). When Start Reduced Scan = 0 the reduction
takes place over all lines including vertical flyback.
b) control bits VR1, VR0 = 00 (no reduction of vertical size)
If Start Reduced Scan > Start Vertical Scan the D/A conversion of the saw-tooth
starts (Start Reduced Scan - Start Vertical Scan) lines after begin of the
calculation. This causes a jump of the output voltage VD+, VD- from flyback to scan
level. It may be useful to hide the automatic cut-off control lines if no overscan is
desired (e.g. for VGA display). If Start Reduced Scan <= Start Vertical Scan this
byte has no effect.
Semiconductor Group
25
1998-02-01