PCE84C886 datasheet(42/56 Pages) PHILIPS

42 / 56 page

1996 Jan 08

Philips Semiconductors

Preliminary speciﬁcation

Microcontroller for monitor OSD

and auto-sync applications

PCE84C886

13 TO FORMAT THE OSD

13.1

Number of characters per row

The number of characters per row is a function of

character width. The width of the character displayed is

only dependent upon the value held in the 7-bit

programmable counter (PLLCN) and is not affected by a

change in horizontal resolution (any change in fHsync will be

reflected by a linear change in the frequency of the OSD

clock).

The maximum number of characters per row can be

determined by calculating the number of OSD clock pulses

that occur during the Hsync active period and dividing the

result by the number of horizontal dots in the character

matrix (which is 12). If Hsync is assumed to be active for

85% of its cycle period then the maximum number of

characters per row (N) can be calculated as follows:

13.2

Number of rows per frame

The number of rows per frame is a function of character

height and the spacing between the rows of characters.

The height of a character displayed on the screen is

determined by the number of visible scan lines per frame

and the character size. The number of scan lines is

dependent upon the resolution of the monitor; character

size is selected by the user (see Section 10.1.2). The

PCE84C886 also provides a choice of four inter-line

spaces: 0H, 4H, 8H and 12H (see Section 10.1.2).

If the inter-line spacing is assumed to be zero then the

number of rows per frame (R) can be calculated by dividing

the number of visible scan lines (SL) by the character size

(CS) and dividing the result by the number of vertical dots

in the character matrix (which is 18). This can be

expressed mathematically as follows:

Table 35 shows the number of rows per frame for different

horizontal resolutions.

0.85

OSD

Hsync

-----------------------------

---------------------

13.3

Character size selection for different display

resolutions

To cater for the variable display resolutions (640 x 400,

640

× 480, 800 × 600, 1024 × 768 and 1 280 × 1 024) of

auto-sync monitors, the PCE84C886 offers a choice of 4

different character sizes: 1H/1V, 1H/2V, 1H/3V and 1H/4V.

This allows the height of displayed characters to be of

similar size even when the monitors resolution is changed

(see Table 35).

Table 35 Recommended character size selection for

different display resolutions

RESOLUTION

CHARACTER

SIZE

ROWS/FRAME

640

× 400

1H/2V

640

× 480

1H/2V

800

× 600

1H/3V

1 024

× 768

1H/4V

1280

× 1024

1H/4V

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