ORS § 136.643
In the trial of or examination upon any indictment, complaint, information or other proceeding before any court, magistrate, jury or other tribunal against a person accused or charged with the commission of a crime, the person so charged or accused shall, at the own request of the person, but not otherwise, be deemed a competent witness, the credit to be given to the testimony of the person being left solely to the jury, under the instructions of the court, or to the discrimination of the magistrate, grand jury or other tribunal before which such testimony is given. The waiver of the person of this right creates no presumption against the person. The defendant or accused, when offering testimony as a witness in the own behalf of the defendant, gives the prosecution a right to cross-examination upon all facts to which the defendant or accused has testified and which tend to the conviction or acquittal of the defendant or accused.
ORS 136.643