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Appendix
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
RF auto
RF Forced
AV 1 Auto
AV 1 Auto 16:9
AV 1 forced
AV 2
SVHS
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.
-Controller pin 8 Status
Input - High Impedance
Input - High Impedance
Input - High Impedance
Input - High Impedance
Output - Push Pull
Output - Push Pull
Output - Push Pull
- 27 -
Service manual WP-795
Level
< 1V
not defined
> 2.7 V
1 V < x < 2.7 V
Max. 3.3V
< 0.2 V
< 0.2 V
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