On-Screen Display; Introduction - Motorola MC68HC05T16 Technical Data Manual

9

ON-SCREEN DISPLAY

9.1

Introduction

The PLL-based On-Screen Display module displays programmable number of rows of symbols,
be them characters or graphic symbols, either in a 16x16 dot matrix or in a 12x16 dot matrix over
a full TV screen. It supports double scan mode for TV broadcast systems which implement
non-interlaced scan broadcast. In double scan mode, each horizontal line in the character dot
matrix will be displayed twice. Users have to determine if the target TV system is an interlaced or
non-interlaced TV system. Auto TV system detection is not implemented.
The essence of this OSD module consists of four row buffers for displaying screen characters; with
each row buffer having its own vertical position registers. Row buffers are refreshed if more than
four rows of display are required. The PLL enables the OSD to adapt to any shift or change in the
incoming horizontal flyback frequency. Frame display fade-in and fade-out features are supported
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for smooth display appearance and disappearance.
Besides the 128-character ROM/EPROM for fixed character patterns, there is a 16-character RAM
for user defined patterns. This character RAM can be written and read by the CPU, but read-only
by the OSD hardware. Since the contents of this character RAM can be changed during run-time,
the user can have a large number of character sets stored in internal ROM, or in external
ROM/EPROM/EEPROMs and have them load in via the M-bus.
The character dot matrix can be programmed to be either 12x16 or 16x16. Mixture of character
dot matrices is not permissible on a row. There is no space between adjacent character dot
matrices. The 12x16 dot matrix is mainly used for English-type characters; whereas the 16x16
dot matrix is mainly used for character sets requiring bigger dot matrix to create legible fonts, such
as Korean, Chinese, and Kanji. Each row buffer can display 32 characters for a 12x16
configuration, and 24 characters for a 16x16 configuration.
Character blinking, black-edge (bordering or shadowing), and background color features are
supported. Background and blinking features are on per character basis; whereas bordering
feature is on per row basis. Users have to be careful while designing their character fonts so that
bordering effect is not nullified between adjacent characters in the same row or in two consecutive
rows.
TPG
MC68HC05T16 ON-SCREEN DISPLAY MOTOROLA
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