83C055 Philips Semiconductors, 83C055 Datasheet - Page 23

• Manufacturer Part Number: 83C055
• Description: Microcontrollers for TV and video MTV
• Manufacturer: Philips Semiconductors

Philips Semiconductors
13.8
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
2. The OSD feature can be toggled between this state and ‘active display’ as desired to achieve real-time special effects
3. Since VID2 to VID0 are driven with the current background colour during this time, except during the foreground
1996 Mar 22
Mode1 Mode0
Microcontrollers for TV and video (MTV)
0
0
1
1
visual effects for the duration of the current video field (until the next VSYNC).
such as ‘vertical wiping’.
portion of displayed characters, this produces text against a solid background. This mode is useful for extensive
displays that require user concentration.
2 to 0
BIT
Wc
7
7
6
5
4
3
OSD Control Register OSMOD
0
1
0
1
Mode 0 The OSD feature is disabled. VCLK oscillator is disabled, VID2 to VID0 are set to black, and
Mode 1 The VCLK oscillator is enabled and the OSD logic operates normally internally, but
Mode 2 Normal OSD operation. Active characters can be shown against TV video (for characters
Mode 3 Characters can be displayed but all of the receiver’s normal video is inhibited by holding
6
SHM2 to SHM0
SYMBOL
Mode1
Mode0
Wc
VCTRL is held inactive.This is the mode to which the 83C055 OSD logic is reset; note 1.
VID2 to VID0 are set to black and VCTRL is held inactive; note 2.
with B = 0) or (for characters with B = 1) against a background of the colour defined as an
attribute of BSpace and SplitBSpace characters.
VCTRL asserted throughout the active portion of each scan line; see note 3.
Mode1
5
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.
Reserved.
Display mode select bits; see Table 27.
Reserved.
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.
Mode0
4
23
DISPLAY MODE
3
DESCRIPTION
SHM2
2
83C145; 83C845
83C055; 87C055
SHM1
1
Product specification
SHM0
0