30.10 Code Protection and CodeGuard™ Security

dsPIC33CK512MPT608 family devices offer multiple levels of security for protecting individual intellectual property. The program Flash protection can be broken up into three segments: Boot Segment (BS), General Segment (GS) and Configuration Segment (CS). Boot Segment has the highest security privilege and can be thought to have limited restrictions when accessing other segments. General Segment has the least security and is intended for the end user system code. Configuration Segment contains only the device user configuration data, which are located at the end of the program memory space.

The code protection features are controlled by the Configuration registers, FSEC and FBSLIM. The FSEC register controls the code-protect level for each segment and if that segment is write-protected. The size of BS and GS will depend on the BSLIM[12:0] bits setting and if the Alternate Interrupt Vector Table (AIVT) is enabled. The BSLIM[12:0] bits define the number of pages for BS, with each page containing 1024 IW. The smallest BS size is one page, which will consist of the Interrupt Vector Table (IVT) and 512 IW of code protection.

If the AIVT is enabled, the last page of BS will contain the AIVT and will not contain any BS code. With AIVT enabled, the smallest BS size is now two pages (2048 IW), with one page for the IVT and BS code, and the other page for the AIVT. Write protection of the BS does not cover the AIVT. The last page of BS can always be programmed or erased by BS code. The General Segment will start at the next page and will consume the rest of program Flash, except for the Flash Configuration Words. The IVT will assume GS security only if BS is not enabled. The IVT is protected from being programmed or page erased when either security segment has enabled write protection.

The different device security segments are shown in Figure 30-2. Here, all three segments are shown, but are not required. If only basic code protection is required, then GS can be enabled independently or combined with CS, if desired.