83C145 Datasheet, PDF (23/40 Pages) NXP Semiconductors – Microcontrollers for TV and video MTV

Philips Semiconductors
Microcontrollers for TV and video (MTV)
Product specification
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)
7
6
5
4
3
Wc
−
Mode1
Mode0
−
2
SHM2
1
SHM1
0
SHM0
Table 26 Description of OSMOD bits (see note )
BIT
7
6
5
4
3
2 to 0
SYMBOL
Wc
−
Mode1
Mode0
−
SHM2 to SHM0
DESCRIPTION
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.
Table 27 Selection of Display Modes
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.
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.
1996 Mar 22
23