Does a trial court have jurisdiction to continue to issue findings after a notice of appeal has been filed?

Appellant cites Supple v. Luckenbach, 12 Cal.2d 319, 84 P.2d 52, as authority for the right of a trial court to file findings after an appeal has been taken. The appellate court in that case, however, dismissed the appeal as having been prematurely filed. The only valid judgment therein involved was rendered subsequent to the filing of the appeal. The case is not authority for the proposition that the trial court retains jurisdiction to perform further acts after the filing of a valid notice of appeal.