ST6387 datasheet(45/84 Pages) STMICROELECTRONICS

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ST6365, ST6375, ST6385 ST6367, ST6377, ST6387

4.6 AFC A/D COMPARATOR

The AFC macrocell contains an A/D comparator

with five levels at intervals of 1V from 1V to 5V.

The levels can all be lowered by 0.5V to effectively

double the resolution.

4.6.1 A/D Comparator

The A/D used to perform the AFC function (when

high threshold is selected) has the following volt-

age levels: 1,2,3,4 and 5V. Bits 0-2 of AFC result

nary form (less than 1V is 000, greater than 5V is

101).

If the application requires a greater resolution, the

sensitivity can be doubled by clearing to zero bit 2

of the OUTPUTS control register, address E5h. In

this case all levels are shifted lower by 0.5V. If the

two results are now added within a software rou-

tine then the A/D S-curve can be located within a

resolution of 0.5V.

The A/D input has high impedance able to with-

stand up to 13V signals (input level tolerances

± 200mV absolute and ± 100mV relative to 5V).

Figure 30. AFC Input Configuration

AFC, IR and OSD Result Register (AFCR)

Address: E4h - Read only

Reset Value: 00h

D7-D5. These bits are not used.

VSYNC. This bit reads the status of the VSYNC

pin. It is inverted with respect to the pin.

IR. This bit reads the status of the IR latch. If a sig-

nal has been latched this bit will be high.

AD2-AD0. These bits store the real time conver-

sion of the value present on the AFC input pin. Un-

defined reset value.

AFC Shift Register (AFSR)

Address: E4h - Write only

Reset Value: 00h

D7, D6, D5, D4, D3, D1, D0. These bits are not

used.

ADCR3. This bit determines the voltage range of

the AFC input. Writing a zero will select the 0.5V to

4.5V range. Writing a one will select the 1.0V to

5.0V range. Undefined after reset.

Caution: This register contains at least one write

only bit. Single bit instructions (SET, RES, INC

and DEC) should not be used.

VA00458

AFC

AFC (INPUT, HIGH IMPEDANCE)

VSYNC

AD2

AD1

AD0

ADSR3

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