STV9118 datasheet(26/46 Pages) STMICROELECTRONICS

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STV9118

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Figure 2. Horizontal sync signal

10.2.2 - Sync. presence detection flags

The sync. signal presence detection flags in the

status register (VDet, HVDet, VExtrDet) do not

show in real time the presence or absence of the

corresponding sync. signal. They are latched to 1

as soon as a single sync. pulse is detected. In or-

der to reset them to 0 (all at once), a 1 must be

written into SDetReset I2C bus bit, the reset action

taking effect with ACK bit of the I2C bus transfer to

the register containing the SDetReset bit. The de-

tection circuits are then ready to capture another

event (pulse). See Note 47.

Figure 3. Extraction of V-sync signal from H/V-sync signal

10.2.3 - MCU controlled sync. selection mode

I2C bus bit VSyncAuto is set to 0. The MCU reads

the polarity and signal presence detection flags,

after setting the SDetReset bit to 1 and an appro-

priate delay, to obtain a true information of the sig-

nals applied, reads and evaluates this information

and controls the vertical signal selector according-

ly. The MCU has no access to polarity inverters,

they are controlled automatically.

See also chapter I2C BUS CONTROL REGISTER

MAP on page 21.

10.2.4 - Automatic sync. selection mode

I2C bus bit VSyncAuto is set to 1. In this mode, the

device itself controls the I2C bus bits switching the

polarity inverters (HVPol, VPol) and the vertical

sync. signal selector (VSyncSel), using the infor-

mation provided by detection circuitry. If both ex-

tracted and pure vertical sync. signals are present,

the one already selected is maintained. No inter-

vention of the MCU is necessary.

10.3 - HORIZONTAL SECTION

10.3.1 - General

The horizontal section consists of two PLLs with

various adjustments and corrections, working on

horizontal deflection frequency, then phase shift-

ing and output driving circuitry providing H-drive

signal on HOut pin. Input signal to the horizontal

section is output of the polarity inverter on H/

HVSyn input. The device ensures automatically

that this polarity be always positive.

10.3.2 - PLL1

The PLL1 block diagram is in Figure 5. It consists

of a voltage-controlled oscillator (VCO), a shaper

with adjustable threshold, a charge pump with inhi-

bition circuit, a frequency and phase comparator

and timing circuitry. The goal of the PLL1 is to

make the VCO ramp signal match in frequency the

sync. signal and to lock this ramp in phase to the

sync. signal, with a possibility to adjust a perma-

nent phase offset. On the screen, this offset re-

Positive

Negative

tPulseHSyn

H/V-sync

Integration

Extracted

textrV

tPulseHsyn

V-sync

Internal

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