Source Switching; Controller I/O Pin Configuration And Function - NEC DTE-29U1TH Service Manual

Service Manual CP-785F

5-3 Source switching

The TDA936x has only one external video input, the external video switching circuit made with
IA01(Video Switching IC)allows 3 external video signal inputs. The switching command can be
the -Controller pin 8 and pin 4 when the software takes control of the video source.
The -Controller pin 8 and pin 4 is automatically configured by the controlling software (See table
below).
The controlling software via I2C bus selects the signal source :
- Video signal from tuner ( Pin 40 ).
- External video ( AV1, AV2, DVD ) depending on IA01(Video Switching IC)
The sound source switching is done in the MSP341XD ( I601 ), by the -Controller via I2C bus.

5-4 -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.
Push-Pull
The push pull mode can be used for output only. Both sinking and sourcing is active, which
leads to sleep slopes. The levels are 0 and Vddp, the supply voltage 3.3Volts.
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