ST72734 datasheet(76/144 Pages) STMICROELECTRONICS

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ST72774/ST727754/ST72734

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TIMING MEASUREMENT UNIT (Cont’d)

– Obtain the minimum number of horizontal

sync output pulses (V2) between the last fall-

ing edge of the active video input (AV) and the

rising edge of the vertical sync signal (VSYN-

CO or VFBACK) during two 2 consecutive

frames.

The

H_V

bit

selects

horizontal

vertical

measurement. This selection should be made prior

to starting the measurement by setting the START

bit. This bit is set by software but only cleared by

hardware at the end of the measurement.

When the measurement is finished (rising edge of

AV, horizontal or vertical sync signals), the results

(T1,T2) are transferred into the corresponding

registers (H1,H2) or (V1,V2).

Note: The values of the H1/H2 or V1/V2 registers are

available only at the end of a measurement (after

the START bit has been cleared).

4.5.3.1 Horizontal Measurement

When the H_V bit = 1, and when the START bit is

set by software, the measurement starts after the

next vertical sync pulse. The TMU searches the

minimum values of H1 and H2 until the rising edge

of the next following vertical sync pulse. The

START bit is then cleared by hardware.

The values of the H1 and H2 registers are

available only at the end of a measurement, in

other words when the START bit is at 0.

4.5.3.2 Vertical Measurement

When the H_V bit = 0 and, when the START bit is

set by software, the TMU measures the minimum

V1 and V2 values during 2 consecutive vertical

frames. The START bit is then cleared by

hardware.

4.5.3.3 Special cases

– If an overflow of the counter occurs during any of

the measurements, the measured T1 or T2 val-

ues will be 7FFh.

– If the AV signal is always low (no active video),

the measured T1 or T2 values will also be 7FFh.

– If T1

≤ 0 (AV already high when the falling edge

of the sync signal occurs), the measured T1 val-

ue will be fixed to 1.

– If T2

≤ 0 (AV still high when the rising edge of the

sync signal occurs), a specific T2 value will be re-

turned.

Note: Refer to Application Note AN1183 for further de-

tails.

Figure 48. Horizontal Measurement

Figure 49. Vertical Measurement

HSYNCO or

H1 and H2 measured in oscillator clock periods

Note: HSYNCO or HFBACK must be positive.

HFBACK

VSYNCO or

V1 and V2 measured in horizontal pulses

Note: VSYNCO or VFBACK must be positive.

VFBACK

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