8
AK - 44
CHASSIS
2.9 µ-Controller
The ST92195 is the micro-controller, which is required for a color TV receiver. ST92195D1 is the version with one page
Teletext and ST92195D7 is the one with 7 page Teletext. The IC has the supply voltage of 5 V and they are mounted in
PSDIP package with 56 pins.
µ-Controller has the following features
- Display of the program number, channel number, TV Standard, analogue values, sleep timer, parental control and
mute is done by OSD
- Single LED for stand-by and on mode indication
- System configuration with service mode
- 3 level logic output for SECAM and Tuner band switching
IC 501 controls all the functions of the receiver operated by the remote control and the front panel customer controls. It
produces the on screen graphics, operates tuning, customers controls and engineering controls, and also incorporates
all of the Teletext functions. It also controls the video processor, the audio processor, and the tuner. The circuits just
mentioned are controlled via the I²C bus. Also IC501 controls the video source switching, vertical position adjustment
and the vertical linearity adjustment via its ports.
An external 8K EEPROM is used by the micro. The EEPROM comes fully programmed. The main clock oscillator is 4.0
MHz crystal X501 on pins 50 and 51. Reset is provided on pin 2 via Q504. On switching on pin 2 becomes high and the
controller gets reset which stays valid till a low signal comes on that pin.
2.9.1 Controls
Command information from the infrared remote controller is fed through the sensor IC502 to pin 1 of the micro-
processor. Operation of the customer front panel keys is detected by pin 8 that is an ADC (analogue to digital
converter). Pressing a switch will connect the 5V to the ground through a particular resistor that determines the
value of the voltage on pin8 at that instant. This obtained value is comprehended by the micro and the corre-
sponding operation is performed. Refer to the following table:
Button Theoretical
voltage
Resistance
P+
3.0V
R502
P- 4.0V
R503
V+ 2.0V
R504
V- 1.5V
R506
Menu 1.0V R505
IC501 automatically switches from TV mode to AV1 by detecting the signal from or pin8 at the Scart connector,
through it 56 pins. The picture mode is determined according to the following table:
Direct Voltage
Picture mode
0 ~ 2 V
TV
4,5 ~ 7 V
16 :9
9,5 ~ 12 V
4 :3
2.9.2 Teletext
The microprocessor IC501 performs all of the Teletext functions internally. The Composite blanking video and
Sync signal (CBVS) is input to pin 33 of the micro from pin 29 of IC403. When text is selected the text graphics
are output as R.G.B signals on pins 15/16/17 of the micro and fed to pins 34/35/36 of IC403. At the same time
pin 18 of the micro goes high taking pin 37 of IC403 high, blanking the picture and selecting text R.G.B. input.
Note: mixed mode is available and fast text with 8-page memory.
Summary of Contents for 21LF-90N
Page 6: ...6 21LF 90N CHASSIS LAYOUT Mother Unit CRT Unit Headphone Unit ...
Page 48: ...36 AK 44 CHASSIS 1 I H G F E D C B A 2 3 4 5 6 7 18 4 Schematic Diagram of Audio Circuit ...
Page 52: ...40 AK 44 CHASSIS 1 I H G F E D C B A 2 3 4 5 6 7 18 7 Schematic Diagram of CRT Socket Circuit ...
Page 55: ...43 AK 44 CHASSIS Notes ...
