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How should the OSCSEL pin be handled in QzROM version?

Latest Updated:09/29/2006

Question:

(Pin)  How should the OSCSEL pin be handled in QzROM version? [2006/09/29]

Answer:

(1) When OSCSEL = L
Connect the OSCSEL pin in the shortest and closest GND pattern to the GND supplying the VSS pin of the microcomputer. In addition, connecting a resistor of approximately 5kΩ in series to the GND may improve noise tolerance. In this situation, connect the pin in the shortest and closest GND pattern to the GND supplying the VSS pin of the MCU, as above.

(2) When OSCSEL = H
Connect the OSCSEL pin in the shortest and closest VCC pattern to the VCC supplying the VCC pin of the microcomputer. In addition, connecting a resistor of approximately 5kΩ in series to the VCC may improve noise tolerance. In this situation, connect the pin in the shortest and closest VCC pattern to the VCC supplying the VCC pin of the MCU, as above.

(Explanation)
The OSCSEL pin of the QzROM version is the power source input pin for the built-in QzROM. When programming in the QzROM, the impedance of the OSCSEL pin is kept low to allow the writing current to flow into the built-in QzROM. Because of this, noise can enter easily. If noise enters the OSCSEL pin, instruction codes or data are not read correctly from the QzRoM, which may cause malfunction.

(#106390)

Suitable Products
38D2
38D5