PCA8515P Philips Semiconductors, PCA8515P Datasheet - Page 47

• Manufacturer Part Number: PCA8515P
• Description: Stand-alone OSD
• Manufacturer: Philips Semiconductors

Philips Semiconductors
12 OSD CLOCK SELECTION FOR DIFFERENT TV
12.1
The PCA8515 supports three different TV scanning
standards. To obtain the best quality character display,
each TV standard requires a different OSD frequency. To
cater for this requirement the PCA8515 provides a
programmable OSD clock that generates frequencies in
the range 4 to 10 MHz. The two examples given below
illustrate the OSD clock requirements for different TV
scanning standards.
12.1.1
The OSD clock is applied directly to the OSD circuitry and
can take any value within the 4 to 10 MHz range. The
NTSC 525LPF/60 Hz standard when used with a 19 inch
screen and an OSD clock of 8 MHz produces a character
dot width of 13.2 mm.
12.1.2
With this standard, in order to obtain the same character
dot width as in the NTSC 525LPF/50 Hz example given
above; the OSD clock must be doubled.
HSYNC is applied directly to the OSD circuitry without
being divided by two as both the horizontal frequency
(1250 Hz) and the vertical frequency (100 Hz) are
doubled.
12.2
The number of characters per row is a function of the OSD
clock frequency and the TV standard used.
With reference to Fig.40 the active video signal period of a
horizontal line is 53.5 s. However, in order to reduce
jittering at the screen edge, overscan is normally applied
by the TV manufacturer and this reduces the visible video
signal period to 48.15 s. The examples given below show
how the number of characters per row and the character
width may be obtained for the NTSC 525LPF/60 Hz
TV standard using different OSD clock frequencies.
12.2.1
1995 Jan 19
As f
The number of visible dots on one horizontal line is 290
(48.15 s/0.1666 s). However, as the starting position
of the first character dot is approximately 45 dots after
HSYNC, the actual visible number of dots per line is 245.
Stand-alone OSD
STANDARDS
OSD
OSD frequency
Maximum number of characters per row
NTSC 525LPF/60 Hz and PAL 625LPF/50 Hz
PAL 1250LPF/100 Hz
NTSC 525LPF/60 Hz; f
= 6 MHz; T
OSD
= 0.1666 s
OSD
= 6 MHz
47
12.2.2
12.3
The number of rows per frame is a function of the number
of active lines per display field and the number of vertical
dots in the character matrix (which is 18). The number of
rows per frame (N) is calculated as shown below.
The three examples shown below illustrate how the
maximum number of rows per frame is obtained for each
TV scanning standard.
12.3.1
The number of active lines per field for this standard is
between 241.5 and 249H (see Fig.41). If the value of 241
is used then the maximum number of rows per frame is 13.
12.3.2
The number of active lines per field for this standard is 280.
Therefore, the maximum number of rows per frame is 15.
12.3.3
With this standard it is not necessary to divide HSYNC by
two as both the horizontal and vertical frequency are
doubled. The maximum number of rows per frame is 15.
Each character is composed of a 12
therefore the maximum number of charcters on one line
is 20 (245/12).
If a 19 inch TV screen is used, the width of a horizontal
line is approximately 370 mm and this gives a character
width of 18.5 mm.
As f
The number of visible dots on one horizontal line is 481
(48.15 s/0.1 s). Allowing for the initial starting position
of 45 dots, the actual number of visible dots per line is
436.
Each character is composed of a 12 x 18 dot matrix;
therefore the maximum number of charcters on one line
is 36.
If a 19 inch TV screen is used, the width of a horizontal
line is approximately 370 mm and this gives a character
width of 10.3 mm.
N
=
OSD
Maximum number of rows per frame
number of active lines per field
-------------------------------------------------------------------------------- -
NTSC 525LPF/60 Hz; f
NTSC 525LPF/60 H
PAL 625LPF/50 H
PAL 1250LPF/100 H
= 10 MHz; T
18
OSD
= 0.1 s
Z
Z
Z
OSD
Preliminary specification
= 10 MHz
PCA8515
18 dot matrix;