NEC MultiSync LCD1550V Service Manual page 72

1. Power Circuit
1.1 Power input block (Circuit diagram: SW REG board)
A power supply for internal 12V and 5V are gained from the power connector through the voltage
supervisory circuit.
1.2 Power control block
1.2.1 Basic power control (Circuit diagram: MAIN Board )
SW REG board is used to generate the system power. It have built in PWM controllers to provide two
voltage output, one is provided for microprocessor or other TTL level IC (+5V) etc., the other one is provided
for the power of inverter (+12V). These two supply power used the same oscillation frequency, the same
start-up circuit, and the same protection circuit, so they can avoid the interference each other.
1.2.2 3.3V power control (Circuit diagram: MAIN Board P.4/5)
The U11,U10 are DC converter for the 3.3V power system. It output fixed 3.3V. The U16 is a DC converter
for 2.5V power system. It out fixed 2.5V.
3.3V power are fed to S9050,and panel. 2.5V power is only fed to S9050.
1.2.3 LCD panel 3.3V power control (Circuit diagram: MAIN Board P.5/5)
Panel power control used Q6 and U15 from S9050(pin_94) PENVDD.
When the PENVDD stays at the high level, the Panel voltage is 3.3V .
When the PENVDD stays at the low level, the Panel voltage is 0V .
2. Microcomputer Control Circuit
2.1 Clock circuit (Circuit diagram: MAIN Board P.3/5)
The Y1 is a crystal the microcomputer. It generates an output of 14.318MHz.
2.2 Microcomputer port circuit (Circuit diagram: MAIN Board P.3/5 and P.1/5)
S9050 has an embedded Microcontroller link to U8 Flash Rom.
2
2.2.1 I C buses
U3 (PIN40) (GPIO2) SDDAT
U3 (PIN39) (GPIO1) SDCLK
2
This is an I C serial communication bus and is used for R or W data communication of U2 and U9.
2.2.2 S9050 and Flash ROM communication buses
U3 (PIN75) MCAD0
U3 (PIN74) MCAD1
U3 (PIN73) MCAD2
U3 (PIN72) MCAD3
U3 (PIN71) MCAD4
U3 (PIN70) MCAD5
U3 (PIN69) MCAD6
U3 (PIN68) MCAD7
U3 (PIN67) MCA8
U3 (PIN57) MCA9
U3 (PIN56) MCA10
Serial data
Serial clock
U3 (PIN55) MCA11
U3 (PIN54) MCA12
U3 (PIN53) MCA13
U3 (PIN52) MCA14
U3 (PIN51) MCA15
U3 (PIN50) MCAD16
U3 (PIN49) MCAD17
U3 (PIN61) CS0#
U3 (PIN60) MCWR#
U3 (PIN59) MCRD#
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