p87c770 ETC-unknow, p87c770 Datasheet - Page 45

• Manufacturer Part Number: p87c770
• Description: Microcontrollers Ntsc With On-screen Display Closed Caption
• Manufacturer: ETC-unknow

Philips Semiconductors
18.5
These controls are used for defining the display areas.
Two types of areas are possible. One area is static and
controlled via the main row counter, while the other is
dynamic and can be soft scrolled. The areas cannot cross
each other. Only one soft scroll area is possible.
A scroll map is provided which is addressed by the display
row and contains the address of the data in the memory
that is to be displayed. A bit is also provided to enable the
text display, outside of the scroll area.
Outside the defined scroll area, the scroll map is
addressed by the main row counter. Within the visible soft
scroll area, the scroll map is addressed by the scroll row
counter. The text display enable bit within this area is
ignored.
The number of rows that can be scrolled through can be
set by defining the start row (scroll map value) and end
row. The defined number of rows should be at least one
more than the visible scroll area height.
The height of the visible area is defined as a number of
rows. The position of the scroll area is defined as an offset
in number of rows from the start of the text area.
The values programmed into the registers must ensure a
sensible display. the following should be noted:
18.5.1
The soft scrolling function is done by modifying the start
count of the row scan-line count of the first scroll row. This
is decremented once per frame automatically thus
providing the effect of the top row disappearing while the
bottom row is appearing.
1999 Jun 11
If values are programmed that cause the display to go
beyond the vertical sync signal, the display will stop and
react as if finished
If the visible scroll area is made larger than the number
of rows allocated to the scroll function, then they will
wrap around and be repeated
If the defined range of rows for scrolling is greater than
the scroll area, these rows should not be used for other
display purposes.
Microcontrollers for NTSC TVs with On-Screen
Display (OSD) and Closed Caption (CC)
Text display controls
S
OFT SCROLL ACTION
45
At the count 0, the scroll row counter is incremented
automatically and the line-scan counter is set to 12 again.
This pushes the top row to the bottom. This row must be
cleared by the core during the fly-back period.
If the number of rows allocated to the scroll counter is
larger than the defined visible scroll area, this allows parts
of rows at the top and bottom to be displayed during the
scroll function.
Only screens which contain single height rows or only
double height rows can be scrolled.
18.5.1.1
The soft scroll function is started by writing a logic 1 to the
SCRL bit in the Read Only Status Register (see
Section 18.9.9). This bit will be cleared when the scrolling
of one row is completed.
A hard scrolling action can also be performed when writing
a logic 0 to the SCRL bit in the Write Only Status Register.
If a logic 0 is written to this bit, the display in the scroll area
is subsequently shifted up by one row.
Table 61 Soft scroll enable
18.5.1.2
The SCON bit in the Status Register controls whether a
scroll area is active or not. The default value is no scroll
area enabled, and the display is controlled only by the
scroll map entries. When this bit is set to a logic 1 the scroll
area is activated and the values contained in the SSACR,
SRRR and STA registers take effect.
Table 62 Soft scroll area enable
SCON
SCRL
0
1
0
1
Soft scroll enable
Soft scroll area enable
Activates hard scroll, shifts display in one
row increment, stops soft scroll.
Start scrolling function.
no scroll area enabled
scroll area enabled
SOFT SCROLL AREA
SOFT SCROLL
P8xCx70 family
Product specification