September 1990

5

Philips Semiconductors

Preliminary specification

Horizontal/vertical synchronization circuit

TDA2579B

FUNCTIONAL DESCRIPTION

Vertical part (pins 1,2,3,4)

The IC embodies a synchronized divider system for generating the vertical sawtooth at pin 3. The divider system has an

internal frequency doubling circuit, so the horizontal oscillator is working at its normal line frequency and one line period

equals 2 clock pulses. Due to the divider system no vertical frequency adjustment is needed. The divider has a

discriminator window for automatically switching over from the 60 Hz to 50 Hz system. The divider system operates with

3 different divider reset windows for maximum interference/disturbance protection.

The windows are activated via an up/down counter. The counter increases its counter value by 1 for each time the

separated vertical sync pulse is within the searched window. The count is decreased by 1 when the vertical sync pulse

is not present.

Large (search) window: divider ratio between 488 and 722

This mode is valid for the following conditions:

1. Divider is looking for a new transmitter.

2. Divider ratio found, not within the narrow window limits.

3. Up/down counter value of the divider system operating in the narrow window mode decreases below count 1.

4. Externally setting. This can be reached by loading pin 18 with a resistor of 220 k

Ω to earth or connecting a 3.6 V

diode stabistor between pin 18 and ground.

Narrow window: divider ratio between 522-528 (60 Hz) or 622-628 (50 Hz).

The divider system switches over to this mode when the up/down counter has reached its maximum value of 12 approved

vertical sync pulses. When the divider operates in this mode and a vertical sync pulse is missing within the window the

divider is reset at the end of the window and the counter value is decreased by 1. At a counter value below count 1 the

divider system switches over to the large window mode.

Standard TV-norm

When the up/down counter has reached its maximum value of 12 in the narrow window mode, the information applied to

the up/down counter is changed such that the standard divider ratio value is tested. When the counter has reached a

value of 14 the divider system is changed over to the standard divider ratio mode. In this mode the divider is always reset

at the standard value even if the vertical sync pulse is missing. A missed vertical sync pulse decreases the counter value

by 1. When the counter reaches the value of 10 the divider system is switched over to the large window mode.

The standard TV-norm condition gives maximum protection for video recorders playing tapes with anti-copy guards.

No-TV-transmitter found: (pin 18

< 1.2 V)

In this condition, only noise is present, the divider is rest to count 628. In this way a stable picture display at normal height

is achieved.

Video tape recorders in feature mode

It should be noted that some VTRs operating in the feature modes, such as picture search, generate such distorted

rolling picture (see Phase detector, sub paragraph d). In general VTR-machines use a re-inserted vertical sync pulse in

the feature mode. Therefore the divider system has been made such that the automatic reset of the divider at count 628

The divider system also generates the anti-top-flutter pulse which inhibits the Phase 1 detector during the vertical sync.

pulse. The width of this pulse depends on the divider mode. For the divider mode a the start is generated at the reset of

the divider. In mode b and c the anti-top-flutter pulse starts at the beginning of the first equalizing pulse.