Pennsylvania Rule of Evidence 609 pertains to when a witness may be impeached with a prior conviction. Pennsylvania allows for either party, in a criminal case, to impeach any witness with a select category of prior convictions. In Pennsylvania, this select category of prior convictions is known as "crimen falsi." Crimen falsi means crimes involving dishonesty. In order for a crime to be classified as crimen falsi, the offense must involve some element of deceit or dishonesty, ie theft or forgery.
This rule differs from the Federal Rule of Evidence 609, which also deals with impeaching the credibility of a witness. Under the Federal Rules of Evidence, a witness may be impeach with either a conviction for a crime of dishonesty OR a conviction of a crime where the penalty could have been more than one year in prison. Obviously, the main difference between the PA rule and the Federal rule is that the federal rule allows for a broader category of crimes which can form the basis of impeachment.