PCA8514T PHILIPS [NXP Semiconductors], PCA8514T Datasheet - Page 47

• Manufacturer Part Number: PCA8514T
• Description: Stand-alone OSD
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
12 OSD CLOCK SELECTION FOR DIFFERENT TV
12.1
The PCA8514 supports four 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 PCA8514 provides a
programmable OSD clock that generates frequencies in
the range 4 to 14 MHz. The three 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 14 MHz frequency
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/60 Hz standard that
uses an OSD clock of 7 MHz; the OSD clock must be
doubled to 14 MHz because the horizontal frequency is
doubled.
To keep the same character height as that in the
NTSC 525LPF/60 Hz standard, HSYNC is also divided by
two, internally.
12.1.3
With this standard, in order to obtain the same character
dot width as in the PAL 625LPF/50 Hz standard; 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.
1995 Nov 27
Stand-alone OSD
STANDARDS
OSD frequency
NTSC 525LPF/60 Hz and PAL 625LPF/50 Hz
NTSC 1050LPF/60 Hz
PAL 1250LPF/100 Hz
47
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
12.2.2
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.
Each character is composed of a 12
therefore the maximum number of characters 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
therefore the maximum number of characters on one
line is 36.
With a 19 inch TV screen, the width of a horizontal line
is approximately 370 mm and the character width is
10.3 mm.
OSD
OSD
Maximum number of characters per row
NTSC 525LPF/60 Hz; f
NTSC 525LPF/60 Hz; f
= 6 MHz: t
= 10 MHz: t
OSD
OSD
= 0.1666 s.
= 0.1 s.
OSD
OSD
= 6 MHz
= 10 MHz
Product specification
PCA8514
18 dot matrix;
18 dot matrix;