Circuit Description - ViewSonic PerfectFlat E90fB-4 Service Manual

4. Circuit Description

4-1 MICRO CONTROLLER AND DEFLECTION CIRCUIT
MICRO Controller
The micro controller(IC101) core is a 80C51 type. The micro clock frequency of 12 Mhz is derived from the
Xtal oscillator,which is running at 48MHz. The DDC interface is suitable to handle DDC2 by a modified
2
hardware I C-bus interface .Standard high current ports,3 ADC pouts with voltage inputs and 4 static standard 8
bit DAC outputs (low interference) and one PWM output for digital control application are implemented. The
central processing unit (CPU) manipulates operands in two memory spaces.These are the 1024byte internal
data memory(consisting of 256 bytes standard RAM and 768 bytes AUX-RAM) and 48K-byte internal program
memory . The programmemory of the SAA4849 consists of 48K bytes ROM.
The SAA4849P provides sync. Processing with full auto sync. Capability, a flexible SMPS block and an
extensive set of geometry control facilities. Further the IC generates the drive waveforms for DC coupled vertical
boosters to the TDA4863A.
H/V sync signals processor
The functions of the sync processor include polarity detection, H-SYNC & V-SYNC signals counting,
Programmable SYNC signals output, free running signal generator. Pin52/Pin53 are for the H-SYNC and
V-SYNC input. and the polarity are setting in the positive. When no signal input, the Pin49 will output a 75Hz
V-SYNC free run signal. The Pin18/20will output a 60KHz H-SYNC free run signal. for the monitor testing use.
Reset Circuit(pin23)
There are three ways possible to invoke a reset and initialize the SAA4849 micro controller part:
Via power-on reset circuit
Via watchdog timer overflow(only micro controller reset)
Via deflection reset after start up(only micro controller reset)
The reset pin(pin23) is connected to a Schmitt trigger for nose reduction. A reset is accomplished by holding the
Reset pin HIGH.
5V
ViewSonic Corporation
C145
22U
R153
2.7K
10
RST Pin23
C102
0.1UF
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