Even if Apple Computer Inc wants to divest the Newton Personal Digital Assistant business, it needs to keep the franchise fresh if it is not to lose value at a frightening rate. Accordingly, the company has unveiled the MessagePad 130 with user- controllable back lighting for on-demand use and a new non-glare screen for viewing and entering information in any lighting condition. It runs what has been hailed as a much improved Version 2.0 of the Newton operating system and will come bundled with the Newton back-up utility for Windows and Mac OS personal computers; serial cables; pocket Quicken 1.2; Compuserve mail client; Newton tour reference software; and handwriting instruction reference demo. It will ship for $800 next month.