P83C266BDR datasheet(66/92 Pages) PHILIPS

66 / 92 page

1999 Mar 10

Philips Semiconductors

Product speciﬁcation

Microcontrollers for PAL/SECAM TV

with OSD and VST

P8xCx66 family

17.12 Maximum number of characters per row

The number of characters per row is a function of the OSD

clock frequency and the TV standard used.

The active video signal period of a horizontal line is

53.5

µs. 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

µs.

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.

17.12.1 NTSC 525LPF/60 Hz; f

OSD =6MHZ

• As fOSD = 6 MHz; TOSD = 0.1666 µs

• The number of visible dots on one horizontal line is 290

(48.15

µs/0.1666 µs)

• Each character is composed of a 12 x 18 dot matrix;

therefore the maximum number of characters on one

line is 24 (290/12)

• 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 15.4 mm (370/24).

17.12.2 NTSC 525LPF/60 HZ;f

OSD =10MHZ

• As fOSD = 10 MHz; TOSD = 0.1 µs

• The number of visible dots on one horizontal line is 481

(48.15

µs/0.1 µs)

• Each character is composed of a 12 x 18 dot matrix;

therefore the maximum number of characters on one

line is 40

• 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 9.25 mm.

17.13 Maximum number of rows per frame

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 two examples shown below illustrate how the

maximum number of rows per frame is obtained for

different TV scanning standards.

17.13.1 NTSC 525LPF/60 HZ

The number of active lines per field for this standard is

between 241.5 and 249 H. If the value of 241 is used then

the maximum number of rows per frame is 13.

17.13.2 PAL 625LPF/50 HZ

The number of active lines per field for this standard is 280.

Therefore, the maximum number of rows per frame is 15.

number of active lines per field

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