NEC NEC MultiSync LCD1525V LCD1525V LCD1525V, Service Manual

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7-3
7. CPU circuit
I201 (80C51RA2) functions as the CPU.
The source voltage for the device is 5.0V and the system clock frequency 20MHz.
7.1 Detection of POWER switch status
The CPU identifies the ON status of the two power supplies. The identification is made when the power
supply is turned off. For example, if the power supply is turned off with the POWER switch, the POWER
switch must be turned on when activating the power supply again. If the power supply is turned off by pulling
out the power cord, then this power supply can be turned on by connecting the power cord, without pressing
the POWER switch.
7.2 Display mode identification
7.2.1 Functions
(1) Display mode identification
•
The display mode of input signal is identified based on Table 1, and according to the frequency and
polarity (HPOL, VPOL) of horizontal or vertical sync signal, presence of the horizontal or vertical sync
signal, and the discrimination signal (HSYNC_DETECT, VSYNC_DETECT).
•
In MOD [3] [4], inappropriate polarity, composite sync, and sync On green are indentified as MOD [4].
•
When the mode has been identified through the measurement of horizontal and vertical frequencies, the
total number of lines is determined with a formula of “Horizontal frequency/Vertical frequency = Total
number of lines. “Final identification can be made by examining the coincidence of the obtained figure
with the number of lines for the mode identified from the frequency. The boundary number of lines in each
mode is shown in Table 2.
•
When the detected frequency if the sync signal has changed, the total number of lines should be counted
even through it is rge identified frequency in the same mode. Then, it is necessary to examine whether
the preset value for the vertical display position of Item 4-3 has exceeded the total number of lines. If
exceeded, a maximum value should be set up, which does not exceed the vertical display position of Item
4-3.
(2) Power save mode.
•
Vertical frequency : Below 24 KHz
•
Horizontal frequency : 75 KHz or above,
•
VTOTAL : 1027 or mode.
(3) Asset management
As an action for asset management, the potential at the WRITE PROTECT pin is turned to be “H” if there is
a vertical input of vertical frequency (42 Hz
±
1Hz).
For more detailed setting method, refer to 4-6-5-14 (8). During this operation, this system stays in the
Out-Of-Range mode.