28LW-92H (serv.man2) - Sharp TV Service Manual (repair manual). Page 8

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CHASSIS
9.POWER SUPPLY (SMPS) 
The DC voltages required at various parts of the chassis are provided by an SMPS transformer 
controlled by the IC MC44608, which is designed for driving, controlling and protecting switching 
transistor
  of  SMPS. The  transformer  generates  145V for Horizontal output stage, +/-14V for audio 
amplifier, 5V and 3.3V stand by voltage and 8V, 12V and 5V supplies for other different parts of the chassis. 
An optocoupler is used to control the regulation of line voltage and stand-by power consumption. There 
is a regulation circuit in secondary side. This circuit produces a control voltage according to the 
changes in 145V DC voltage, via an optocoupler (TCET1102G) to pin3 of the IC. 
During the switch on period of the transistor, energy is stored in the transformer. During the switch off 
period energy is fed to the load via secondary winding. By varying switch-on time of the power 
transistor, it 
 controls  each  portion  of  energy  transferred  to the secondary side such that the output 
voltage level remains nearly independent of load variations.  
 
10.MICROCONTROLLER SDA55XX 
10.1.General Features 
• Feature selection via special function register 
• Simultaneous reception of TTX, VPS, PDC, and WSS (line 23) 
• Supply Voltage 2.5 and 3.3 V 
• ROM version package PSDIP52-2, PMQFP64-1 
• Romless version package PMQFP100-2, PLCC84-2 
 
10.2.External Crystal and Programmable Clock Speed 
• Single external 6MHz crystal, all necessary clocks are generated internally 
• CPU clock speed selectable via special function registers. 
• Normal Mode 33.33 MHz CPU clock, Power Save mode 8.33 MHz 
 
10.3.Microcontroller Features 
• 8bit 8051 instruction set compatible CPU. 
• 33.33-MHz internal clock (max.) 
• 0.360 ms (min.) instruction cycle 
• Two 16-bit timers 
• Watchdog timer 
• Capture compare timer for infrared remote control decoding 
• Pulse width modulation unit (2 channels 14 bit, 6 channels 8 bit) 
• ADC (4 channels, 8 bit) 
• UART (rxd, txd) 
 
10.4.Memory 
• Non-multiplexed 8-bit data and 16 … 20-bit address bus (ROMless Version) 
• Memory banking up to 1Mbyte (Romless version) 
• Up to 128 Kilobyte on Chip Program ROM 
• Eight 16-bit data pointer registers (DPTR) 
• 256-bytes on-chip Processor Internal RAM (IRAM) 
• 128bytes extended stack memory. 
• Display RAM and TXT/VPS/PDC/WSS-Acquisition-Buffer directly accessible via MOVX 
• UP to 16KByte on Chip Extended RAM (XRAM) consisting of; 
- 1 Kilobyte on-chip ACQ-buffer-RAM (access via MOVX) 
- 1 Kilobyte on-chip extended-RAM (XRAM, access via MOVX) for user software 
- 3 Kilobyte Display Memory 
 
10.5.Display Features 
• ROM Character Set Supports all East and West European Languages in single device 
• Mosaic Graphic Character Set 
• Parallel Display Attributes 
• Single/Double Width/Height of Characters 
• Variable Flash Rate 
• Programmable Screen Size (25 Rows x 33...64 Columns) 
• Flexible Character Matrixes (HxV) 12 x 9...16 
• Up to 256 Dynamical Redefinable Characters in standard mode; 1024 Dynamical Redefinable 
Characters in Enhanced Mode 
• CLUT with up to 4096 colour combinations 
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