STV9425 STMicroelectronics, STV9425 Datasheet - Page 9

• Manufacturer Part Number: STV9425
• Description: Video ICs On-Screen Disp Montr
• Manufacturer: STMicroelectronics
• Type: Multisync On-Screen Display For Monitorr

Specifications of STV9425

• Maximum Operating Temperature: + 70 C
• Package / Case: DIP-24
• Minimum Operating Temperature: 0 C
• Mounting Style: Through Hole
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FUNCTIONAL DESCRIPTION (continued)
Figure 5 : Horizontal Timing
IV - Clock and Timing
The whole timing is derived from the XTALIN and
the SYNCHRO (horizontal and vertival) input fre-
quencies. The XTALIN input frequency can be an
external clock or a crystal signal thanks to
XTALIN/XTALOUT pins. The value of this fre-
quency can be chosen between 8 and 15MHz, it is
available on the CKOUT pin and is used by the PLL
to generate a pixel clock locked on the horizontal
synchro input signal.
IV.1 - Horizontal Timing (see Figure 5)
The number of pixel periods is given by the LINE
DURATION register and is equal to :
[LD[5:0] + 1 ] x 12.
(LD[5:0] : value of the LINE DURATION register).
This value allows to choose the horizontal size of
the characters. The horizontal left margin is given
by the HORIZONTAL DELAY register and is equal
to :
[DD[7:0] + 8] x 3 x T
(DD[7:0] : value of the DISPLAY DELAY register
and T
This value allows to choose the horizontal position
of the characters on the screen. The value of
DD[7:0] must be equal or greater than 4 (the mini-
mum value of the horizontal delay is 36 x T
character periods). The length of the active area,
where R, G, B are different from 0, dependson the
number of characters of the strips.
IV.2 - D to A Timing
The D to A converters of the STV9425/25B/26are
pulse width modulater converter. The frequency of
the output signal is :
and the duty cycle is :
H-SYNC
R, G, B
Character
Period
LD[5:0]
Fixed
DD[7:0]
Given by number
of characters of the strips
PXCK
: pixel period).
PXCK
F
256
XTAL
Vi[7:0]
256
0
1
per cent.
= 4 (min)
2
3
PXCK
n + 1
= 3
= 4n + 2
n + 2
After a low pass filter, the average value of the
output is :
V - Display Control
A screen is composed of successive scanlines gath-
ered in several strips. Each strip is defined by a
descriptor stored in memory. A table of descriptors
allows screen composition and different tables can
be stored in memory at thepage addresses(8 pos-
sible addresses).Two typesof strips are avail a ble :
- Spacing strip : its descriptor (see II) gives the
- Character strip : its descriptor gives the memory
Figure 6 : PWM Timing
V1[7:0]
number of black (FBK = 1 in DISPLAYCONTROL
register) or transparent (FBK = 0) lines.
address of the character codes corresponding to
the 1
attributes (see code format III) are defined by a
succession of codes stored in the RAM at ad-
dresses starting from the 1
descriptor. A character strip can be displayed or
not by using the DE bit of its descriptor. A zoom
can be made on it by using the ZY bit.
n + 3
128
255
0
1
st
n + 4
displayed character. The characters and
Vi
STV9425 - STV9425B - STV9426
256
[7:0]
PWM1 Signal
T
XTAL
V
DD
LD - 1
256 . T
st
XTAL
LD
one given by the
0
1
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