Functional Description

STV9212

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2.2

Video Blanking

The three video channels are simultaneously blanked with the high level of either BLKI or FBLK

signals. BLKI is an internal signal drawn from the signal applied on the BLK pin (H-flyback) as

signal.

BLK Input

The BLK input receives an H-flyback pulse that drives:

q

the video blanking circuitry during scan line retrace,

q

the output clamping stage.

A clipping circuit at the input allows the direct use of a high-voltage H-flyback pulse applied through

remains mandatory. In all cases, the value of this resistor must be such that the sinking and

sourcing currents are limited to 1mA and 100µA, respectively.

Permanent Blanking

The entire TV screen can be blanked for an unlimited amount of time using the software blanking

feature. Both bits

SWBLK and TST1 must be set to 1. The three video outputs are forced to their

Figure 5: BLK Input Pin

Figure 6: Software Blanking

GND

40 to

0 to -10V

Typical

H-Flyback signal

GND

~3V

Signal at BLK pin

(Pin 24)

BLK

24

100V

Normal operation

SWBLK=0, TST1=0

Software blanking in operation

SWBLK=1, TST1=1

Black level

Infra-black level

Video output

channels 1,2,3