1996 Mar 22

21

Philips Semiconductors

Product specification

Microcontrollers for TV and video (MTV)

83C145; 83C845

83C055; 87C055

Notes to the description of OSAT bits

1. The latches in which the E,SR, D, and Sh bits are captured are cleared to zero at the start of each vertical scan. This

means that if the first text line on the screen is a short row, or if it contains either double size or shadowing, the text

must be preceded by a New Line character. Like all such characters, this initial New Line advances the vertical

screen position; the VStart value (see register OSORG; Section 13.9) should take this fact into account.

2. For SplitBSpace, a change in B and Bcolor occurs halfway through the character horizontally.

3. The normal Space character has no effect on the Bcolor value.

4. The Bcolor value is not cleared between vertical scans, so that if a single background colour is all that is needed in

an application, it can be set via a single BSpace character during program initialization, and never changed

thereafter. In order for such a BSpace to actually affect the 83C055 internal Bcolor register the Mode field of the

OSMOD register must be set to ‘01B’ (or higher) so that the OSD hardware is operating (see register OSMOD;

Section 13.8).

Table 22 OSD outputs related to character bit map value, Fcolor, Bcolor and B bits

Notes

1. Bcolor (BC2,BC1,BC0) values ‘000’ and ‘111’ minimize the occurrence of transient states among the VID2 to VID0

outputs.

2. The background colour defined by the most recently encountered BSpace or SplitBSpace character is maintained

on the VID2 to VID0 pins except at the following times:

a) During the active time of HSYNC.

b) During the active time of VSYNC.

c) During those pixels of an active character that correspond to a logic 1 in the character’s bit map.

d) During a ‘shadow’ bit.

CHARACTER BIT MAP VALUE

OSD OUTPUTS (notes 1 and 2)

VID2

VID1

VID0

VCTRL

logic 1

FC2

FC1

FC0

driven active

logic 0

BC2

BC1

BC0

B