我问了德国的BBS，他告诉我Retentive Area 用的是NV-RAM技术，不用电池也可以永久保持。我的目的是在Retentive Area 使用状态标志或者预设时间，如果代码属于非法拷贝则应该停机，know-how-protect使用后虽然不可解读源代码，但下载后可以运行，设定口令的话时间长了自己会忘记的~~所以我想在用know_how_protect + 代码来保护程序~

以下是回贴：
Topic: How long can Retentive Area on S7 315-2 DP hold? (2 of 3), Read 25 times
Conf: SIMATIC S7
From: Technical Support techsupport@ad.siemens.de
Date: Freitag, 26. April 2002 09:40

Due to the technology of the retentive area (socalled nv-ram's, they need no battery!!) there are no time limits. These ram's are holding there information as long no new one are stored, and this without any battery or external power.

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Regards,
Stevens