Daewoo DWP-28W2ZZF Service Manual download pdf (Page 54)

Appendix Service manual WP-795

- 27 -

2-3 Source switching

The TDA936x has only one external video input, the external video switching circuit made with Q504,

Q505, Q507, Q508 and Q509 allows 2 external video signal inputs. The switching command can be either

the SCART1 slow switching pin 8 or the

-Controller pin 8 when the software takes control of the video

source. The

-Controller pin 8 is automatically configured by the controlling software ( See table below ).

This pin is also capable of detecting the 3 Status ( 0, 1A, 1B ) described in SCART specifications for

automatic format switching.

TV mode

-Controller pin 8 Status

Level

RF auto Input - High Impedance < 1V

RF Forced Input - High Impedance not defined

AV 1 Auto Input - High Impedance > 2.7 V

AV 1 Auto 16:9 Input - High Impedance 1 V < x < 2.7 V

AV 1 forced Output - Push Pull Max. 3.3V

AV 2 Output - Push Pull < 0.2 V

SVHS Output - Push Pull < 0.2 V

The controlling software via I2C bus selects the signal source :

- Video signal from tuner ( Pin 40 ).

- External video ( SCART 1 or 2 ) depending on Q508 base level.

- External SVHS from SCART 2.

The sound source switching is done in the MSP3415D ( I601 ), by the

-Controller via I2C bus.

Fast R, G, B insertion : The external R, G, B insertion needs a fast switching and cannot be controlled by

the software ( instruction cycle of 1

sec ). The fast switching pin 16 of SCART 1 is directly connected to

the TV processor pin 45 ( Fast blanking input ). The display is synchronised with the selected video

source, i.e. to get stable R, G, B inserted signal they must be synchronised with the selected video source.

The controlling software only enable or disable ( AV2, SVHS, or Forced RF source selected ) fast

blanking.

2-4

-Controller I/O pin configuration and function

The I/O pins of the

-Controller can be configured in many way. All port functions can be individually

programmed by use of the SFR registers.

Each I/O port pin can be individually programmed in these configurations :

Open drain

In this mode, the port can function as in and output. It requires an external pull-up resistor. The maximum

allowable supply voltage for this pull up resistor is +5V.

So in this mode it is possible to interface a 5 Volt environment like I2C while the

-Controller has a 3.3

Volt supply.

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Daewoo DWP-28W2ZZF Service Manual Page 54

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