Auto Dvi Selection - NEC MultiSync LCD2080UX -BKA Service Manual

2.7.4 Auto DVI Selection

The two EDIDs of "digital" and "analog" of INPUT1 can be selected by any of the two methods of Auto and
Manual.
In the AUTO mode, Pin 14 and Pin 16 are short-circuited when the accessory cable is of DSUB-DVIA. In the
DVID-DVID mode, on the other hand, DVI selection is automatically carried out, utilizing the fact that Pin 16
is for a high impedance.
When the DVI selection is performed in the AUTO mode and the signals are of analog, CKF1 is cut off and
BANKSEL of IC8A1 (Pin 11) is turned low. In this state, the analog EDID is read out. In the digital mode,
QKF1 is turned on, BANKSEL is turned high, and the digital EDID is read out.
A changeover action is taken between AUTO and MANUAL by IC8A5 and IC8A4. This status is maintained
at the potentiometer of IC8A3 even though the power supply has been turned off.
Whether DIGITAL or ANALOG is selected in the manual mode is controlled by the microcomputer IC804
according to the user menu of the OSD. This status is maintained at the potentiometer of IC8A2 even
though the power supply has been turned off.
IC8A2 and IC8A3 are controlled by the microcomputer IC804 through the three wires. /PMCS and /PMCS2
are the chip select ICs, respectively. The U/D is used to determine the direction in which the resistance at
the potentiometer is increased or decreased, in order to secure an increment at the rising edge of /INC.
Since this potentiometer is provided with 16 statuses, the status of high or low is changed over by applying
the 16 pulses.
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