ST72734 datasheet(62/144 Pages) STMICROELECTRONICS

62 / 144 page

ST72774/ST727754/ST72734

62/144

SYNC PROCESSOR (SYNC) (Cont’d)

4.4.6.3 Detecting Signal Polarity

The Sync Processor provides two ways for

checking input signal polarity by polling the latches

or using the 5-bit up/down counter.

Polling check

– HSYNCI polarity detection:

UPLAT/DWNLAT bits in LATR register

These bits are directly connected to the 5-bit

Up/Down counter.

UPLAT=1/ DOWNLAT=0 HSYNCI polarity<0

UPLAT=0/ DOWNLAT=1 HSYNCI polarity>0

– VSYNCI Polarity Detection

– VPOL bit (VSYNCO polarity) in POLR and

– VOP bit (VSYNCO polarity control) in MCR

The delay between VSYNCI polarity changes

and the VPOL bit typically toggles within 4

msecs. The polarity detector includes an

integrator to filter possible incoming VSYNCI

glitches.

5-bit Up/Down Counter Check

for HSYNCI Polarity

This method involves the internal 5-bit up/down

counter.

The counter value (CV4-CV0 bits) is updated with

the 5-bit counter value at every detected edge on

the signal monitored.

It is incremented when the signal is high, otherwise

it is decremented.

– Start the detection phase:

Initialize the 5-bit counter: write '00000' in the

CCR register (CV4-CV0 bits).

Select normal mode on falling edge:

LCV1/LCV0 = 0 in the CCR register.

– Software checks the counter value (CV4-CV0)

after an interrupt (with the signal internally con-

nected or ICAP2) or by polling (timeout 150µs).

Positive polarity: The counter value < 1Fh.

Negative polarity: The counter value =1Fh on

the falling edge.

In case of a composite incoming signal, the

software just has to check that the VSYNCO

period and polarity are stable.

4.4.6.4 Extracting VSYNCO from CSYNCI

In case of composite sync, the Vertical sync output

signal is extracted with the 5-bit up/down counter.

Initially,

the

width

Horizontal

Sync

component pulse is automatically determined by

hardware which defines a threshold for the 5-bit

counter with a possible user-defined tolerance.

The circuit then monitors for any incoming period

greater than this previously captured value. This is

then processed as the VSYNCO signal.

To use the Vsync extractor, the following steps are

necessary:

– Detection of a composite sync signal:

When the UPLAT and DOWNLAT bits in LATR

HSYNCI polarity change is detected.

If these bits are stable during two subsequent

ICAP2 interrupt, the composite sync signal is

stable.

– Defining a threshold:

Select the normal mode (LCV1/LCV0=0 in the

CCR register).

Initialize the counter capture CV4-CV0 to 0.

This automatically measures the HSYNCI pulse

width. It defines a threshold in the CV4-CV0 bits

used by the 5-bit up/down counter.

It also allows to check the HSYNCI polarity

(refer to the “5-bit Up/Down Counter Check”

paragraph.

If a user-defined tolerance is to be added, then

an updated value should be written in the CCR

In a composite sync signal, Hsync and Vsync

always have the same polarity.

– Starting the VSYNCO hardware extraction

mode:

According to the Composite sync polarity, select

the extraction mode (LCV1/LCV0 in CCR

Negative polarity: minimum threshold (00h)

Positive polarity: maximum threshold (1Fh)

Note:

The

extracted

VSYNCO

signal

always

has

negative polarity.

ST72734 数据表(PDF) 62 Page - STMicroelectronics

ST72734 数据表(HTML) 62 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载