ST63140 datasheet(56/86 Pages) STMICROELECTRONICS

56 / 86 page

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LINE

Notes: FT. The format character required for each line. Characters in columns 1 thru 15 are displayed.

Ch. (Byte) Character (Index into OSD character generator) or space character

AVAILABLE SCREEN SPACE

Table 12. OSD RAM Map

Emulator Remarks

There are a few differences between emulator and

silicon. For noise reasons, the OSD oscillator pins

are not available: the internal oscillator cannot be

disabled and replaced by an external coil. In the

emulator, the Character Bank Select register can

be written also with Global Enable bit set, while this

is not allowed in the device.

Application Notes

1 - The OSD character generator is composed of a

dual port video ram and some circuitry. It needs

two input signals VSYNC and HSYNC to syncron-

ize its dedicated oscillator to the TV picture. It gen-

erates 4 output signals, that can be used from the

TV set to generate the characters on the screen.

For instance, they can be used to feed the SCART

plug, providing an adequate buffer to drive the low

impedance (75

Ω) of the SCART inputs.

2 - The Core sees the OSD as a number of RAM

locations (80) plus a certain number of control reg-

isters (6). These 86 locations are mapped in two

pages of the dynamic data ram address range

(0h..3Fh).

In page 5 (load 20h in the register 0E8h), there are

64 bytes of RAM, the ones of the first 4 rows (16

bytes each row, 15 characters per row maximum,

plus an hidden leading formatcharacter). In page 6

(load 40h in register 0E8h), the 16 bytes of the fifth

row

(0..0Fh),

and

the

control

registers

(10h..14h,17h).

3 - The video RAM is a dual port ram. That means

that it can be addressed either from the Core or

from the OSD circuitry itself. To reduce the com-

plexity of the circuitry, and thus its cost, some re-

strictions have been introduced in the use of the

OSD.

a. The Core can Only write to any of the 86 loca-

tions (either video RAM or control registers).

b. The Core can Only write to any of the leading

85 locations when the OSD oscillator is OFF.

Only the last location (control register 17h in

page 6) can be addressed at any time. This is

the Global Enable Register, which contains

only the GE bit. If it is set, the OSD is on, if it is

reset the OSD is off.

4 - The timing of the on/off switching of the OSD

oscillator is the following:

a. GE bit is set. The OSD oscillator will start on

the next VSYNC signal.

b. GE bit is reset. The OSD oscillator will be im-

mediately switched off.

ON-SCREEN DISPLAY (Continued)

ST63140,142,126,156

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