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How to determine if it can cause problems if I use IC for UPD6464A OSD?

Latest Updated:08/01/2005

Question:

For the UPD6464A OSD IC, I input a 1 Vp-p signal for an experiment and it was output unchanged. Is there any problem if I use the IC as is?

Answer:

There is a problem.
To make the input signal 1 Vp-p in the external video signal mode, the level of the internal video signal (character signal) must be adjusted accordingly. Perform the following setting.

1. Internal video signal amplitude control bit VPD = 0
2. Voltage applied to Vcnt pin 2.5 V

Item 1 above can be changed by a command, but item 2 requires modification of the hardware.
The voltage of the pin cannot be changed by a command.

- Forcibly apply 2.5 V to the VCNT pin from an external source.
- Insert a resistor between Vcnt and VDD (+5 V)
to adjust the voltage applied to Vcnt to 2.5 V.

The level of VBSO pin is determined by a voltage-dividing resistor connected between the Vcnt pin and VDD (+5V).
The above two methods may be used to adjust the voltage applied to the Vcnt pin to 2.5 V.

Reference document:
OSD LSIs User's Manual Figure 2-9 in "2.2.3 Video signal output section"

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