1996 Mar 22

23

Philips Semiconductors

Product specification

Microcontrollers for TV and video (MTV)

83C145; 83C845

83C055; 87C055

13.8

OSD Control Register OSMOD

Under some conditions writing to OSMOD while the display is active can cause a temporary flicker during that display

field. This can be avoided by only writing to OSMOD during the vertical sync interval.

Table 25 OSD Control Register OSMOD (address C1H)

Table 26 Description of OSMOD bits (see note )

Table 27 Selection of Display Modes

Notes

1. A direct transition from this mode to ‘active display’ (Mode1, Mode0 = 1X) would result in undefined operation and

visual effects for the duration of the current video field (until the next VSYNC).

2. The OSD feature can be toggled between this state and ‘active display’ as desired to achieve real-time special effects

such as ‘vertical wiping’.

3. Since VID2 to VID0 are driven with the current background colour during this time, except during the foreground

portion of displayed characters, this produces text against a solid background. This mode is useful for extensive

displays that require user concentration.

76543210

Wc

−

Mode1

Mode0

−

SHM2

SHM1

SHM0

BIT

SYMBOL

DESCRIPTION

7

Wc

If Wc = 1, then each displayed character is horizontally terminated after

12 bits have been output, as opposed to after 14 bits if Wc = 0. This

allows text to be ‘packed’ more tightly so that more characters can be

displayed per line. In effect, the 2 bits out of the display ROM, which

would otherwise be the rightmost 2 of the 14, are ignored when Wc is 1.

Clearly, if this feature is to be used, it must be accounted for in the design

of the bit maps in the display ROM.

6

−

Reserved.

5

Mode1

Display mode select bits; see Table 27.

4

Mode0

3

−

Reserved.

2 to 0

SHM2 to SHM0

Shadowing mode (ShMode); determines how characters are shadowed

in rows for which the row attribute Sh = 1 (register OSAT; see Table 21);

for the shadowing modes see Fig.8 and Table 28.

Mode1 Mode0

DISPLAY MODE

0

0

Mode 0 The OSD feature is disabled. VCLK oscillator is disabled, VID2 to VID0 are set to black, and

VCTRL is held inactive.This is the mode to which the 83C055 OSD logic is reset; note 1.

0

1

Mode 1 The VCLK oscillator is enabled and the OSD logic operates normally internally, but

VID2 to VID0 are set to black and VCTRL is held inactive; note 2.

1

0

Mode 2 Normal OSD operation. Active characters can be shown against TV video (for characters

with B = 0) or (for characters with B = 1) against a background of the colour defined as an

attribute of BSpace and SplitBSpace characters.

1

1

Mode 3 Characters can be displayed but all of the receiver’s normal video is inhibited by holding

VCTRL asserted throughout the active portion of each scan line; see note 3.