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On Screen Display
OSD Components
The on screen display circuitry consist of the following major parts:
O n S c r e e n D is p la y P a r t s
P a r t s
I n p u t
I C 3 2 5 1
V e r t ic a l s y n c
M a in
– p in 9 5
M ic r o
H o r iz o n t a l
s y n c – p in 9 7
R e m o t e
c o n t r o l in p u t –
p in 7
I C 3 0 0 5
R G B
V id e o
c h a r a c t e r in f o
P r o c e s s o r
– p in s 5 0 - 5 2
OSD Operation
Character Manufacture
The on screen display circuitry within Main Micro IC3251 places channel
numbers and menu information on the TV screen. To perform this it needs
to identify the picture tube's beam location by using vertical and horizontal
deflection (not station sync) signals. These signals are shaped into 5Vp-
p pulses which are input to IC3251/pins 95 and 97. Without either signal
there would be no OSD.
Main Micro IC3251 provides a visual indication of the user command. To
perform this characters are output as pulses on the respective Or, Og and
Ob outputs.
O u t p u t
P u r p o s e
R , G , B c h a r a c t e r s
G e n e r a t e
p u ls e s fr o m p in s 3 2 -
c h a r a c t e r
3 4 .
p u ls e s .
Y s – F u ll b la n k in g
G e n e r a t e
p u ls e
c h a r a c t e r
w in d o w p u ls e
Y m – ½ b la n k in g
m ix in g p u ls e
R , G , B d r iv e o u t p u t t o
M ix o r r e p la c e
C R T c a t h o d e s
a c t iv e v id e o
w it h c h a r a c t e r s .
49
Character Insertion
To make the display appear clean, the active video is blanked for that mo-
ment while the character is inserted into the scan. The YS signal from
IC3251/pin 21 requests that IC3005/pin 49 perform this full blanking func-
tion. When YS goes high, Q3254 is turned on to place +5V into the video
processor IC3005/pin 49. The active video is blanked and the OSD char-
acter is enabled.
When the menu is called for, the characters are placed on a lower ½
brightness mat. A wide window pulse from IC3251/pin 22 creates this
mat. The 4-volt Ym signal output is reduced to 2V at the video processor
input IC3005/pin 49. When this window pulse is high internally, the active
video is reduced in intensity to create the video mat, as well as enable the
OSD signals on the TV screen.
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