STV9423 データシートの表示（PDF） - STMicroelectronics

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STV9423

MULTISYNC ON-SCREEN DISPLAY FOR MONITOR

STMicroelectronics 

FUNCTIONAL DESCRIPTION (continued)

Figure 5 : Horizontal Timing

H-SYNC

STV9422 - STV9424

R, G, B

0

Character

Period

LD[5:0]

Fixed

DD[7:0]

Given by number

of characters of the strips

1

2

3 n+1 n+2 n+ 3 n +4

= 4 (min)

= 4n + 2

LD - 1 LD

0

1

IV - Clock and Timing

The whole timing is derived from the XTALIN and the

SYNCHRO (horizontal and vertival) input frequen-

cies. The XTALIN input frequencycan be an external

clock or a crystal signal thanks to XTALIN/XTALOUT

pins. The value of this frequency 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 horizontalleft margin is given by the

HORIZONTAL DELAY register and is equal to :

[DD[7:0] + 8] x 3 x TPXCK

(DD[7:0] : value of the DISPLAY DELAY register

and TPXCK : pixel period).

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 TPXCK = 3

character periods). The length of the active area,

where R, G, B are different from 0, depends on the

number of characters of the strips.

IV.2 - D to A Timing (STV9422)

The D to A converters of the STV9422 are pulse

width modulater converter.

The

frequency

of

the

output

signal

is

:

fXTAL

256

and

the

duty

cycle

is

:

Vi[7:0]

256

per

cent.

After a low pass filter, the average value of the

output

is

:

Vi [7:0]

256

⋅

VDD

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 the page addresses (8 pos-

sible ≠ addresses).

Two types of strips are available :

- Spacing strip : its descriptor (see II) gives the

number of black (FBK = 1 in DISPLAY CONTROL

register) or transparent (FBK = 0) lines.

- Character strip : its descriptor gives the memory

address of the character codes corresponding to

the 1st displayed character. The characters and

attributes (see code format III) are defined by a

succession of codes stored in the RAM at ad-

dresses starting from the 1st one given by the

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.

Figure 6 : PWM Timing

V1[7:0]

0

1

P WM1 Signal

tXTAL

256 . tXTAL

128

255

9/15

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