TEA2029 STMICROELECTRONICS [STMicroelectronics], TEA2029 Datasheet - Page 29

• Manufacturer Part Number: TEA2029
• Description: APPLICATION NOTE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

V.6.3.1 - 50/60Hz Standard recognition
This function is performed by two shift registers
which are loaded by sync pulses (if present) and if
these pulses fall within the time interval specific to
each standard. These intervals are called ”Register
Windows” and labeled ”W
Figure 57
A. 50Hz STANDARD RECOGNITION
This identification is considered valid if two suces-
sive sync pulses applied to 50Hz shift register fall
within the 50Hz window ”W
synchronization capture, the first pulse will reset
the counters. The second pulse, if present, will
then trigger the 50Hz identification 20ms later
[I
The identification is not valid if two sucessive 50Hz
pulses are not detected. Identification signal is also
used to reduce the vertical synchronization window
in 50Hz standard thereby offering excellent noise
immunity against noise susceptible to be present
in sync signal and hence good display stability.
B. - 60Hz STANDARD RECOGNITION
This identification is validated after three sucessive
sync pulses at 16.6 s period have been detected.
Figure 58 : Definition of Synchronization Windows and Free-running Periods
D
(50) = 1].
60H z
Sync
1 5. 7 73m s
L 247
16 .6 6ms
W R(60Hz)
1 7. 6 9 6 ms 1 9.7 44ms 2 0. 12 8ms
Mute = 1
Mute = 1
Mute = 1
L 27 7
I
R
D50
No Transmission
60Hz Standard
50 H z
50Hz Standard
(50)” and W
Sync
or VCR Mode
R
(Mute = 0)
I
I
= 0, I
D50
D60
(50)”. At the time of
= 1
= 1
L309
D60
W R(50Hz)
= 0
20ms
R
L315
(60).
W
Reset
W
Reset
W
Reset
W
Reset
Register’s
Window
R
R(WIDE)
R(50)
R(60)
Free-running Period
= 0
L247
60Hz
L277
Three pulses are necessary to ascertain the iden-
tification prior to switching the saw-tooth amplitude.
The identification signal [I
reduce the synchronization window and, in case of
one or two missing pulses close to 60Hz, to set the
free-running frequency.
V.6.3.2 - Vertical synchronization window -
Free-running period
In the absence of sync pulse various free-running
periods are specified. Since vertical scanning must
be always active, these free-running periods must
be higher than those of 50 and 60Hz standards so
as to ensure synchronization.
An other window, allowing synchronization only at
the end of scanning, is also necessary. Upon syn-
chronization, this window will allow vertical flyback
only at the bottom of screen. This window should
be narrow for good noise immunity but also wide
enough to yield, upon synchronization, a capture
time unperceptible on screen.
In our case, as long as no standard identification
takes place the window will remain wide, and once
one of the standards has been identified, the win-
dow will be considerably reduced.
In VCR mode, this window will bealways wide since
frame frequencies delivered in high-speed search,
slow review and picture pause modes are very
much variable and must be taken into considera-
tion.
In the absence of transmission (Mute = 0), synchro-
nization is disabled (so as to avoid incorrect syn-
chronization due to noise) and the free-running
frequency is around 50Hz. This will eliminate the
occurrence of picture overlay at the end of trace at
a lower free-running frequency.
TEA2028 - TEA2029 APPLICATION NOTE
L309 L315
50Hz
L361
D
(60) = 1] is also used to
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