PIC12(L)F1612/16(L)F161X

DS40001720C-page 30

Preliminary

 2013-2014 Microchip Technology Inc.

7.3

Checksum Computation

The checksum is calculated by two different methods dependent on the setting of the CP Configuration bit.

7.3.1

PROGRAM CODE PROTECTION DISABLED

With the program code protection disabled, the checksum is computed by reading the contents of the program memory

locations and adding up the program memory data starting at address 0000h, up to the maximum user addressable

location. Any Carry bit exceeding 16 bits are ignored. Additionally, the relevant bits of the Configuration Words are added

to the checksum. All unimplemented Configuration bits are masked to ‘0’.

7.3.2

PROGRAM CODE PROTECTION ENABLED

Project PropertiesConf:BuildingInsert Checksum in User ID

Memory is checked, then the 16-bit checksum of the equivalent unprotected device is computed and stored in the user

ID. Each nibble of the unprotected checksum is stored in the Least Significant nibble of each of the four user ID

locations. The Most Significant checksum nibble is stored in the user ID at location 8000h, the second Most Significant

nibble is stored at location 8001h, and so forth for the remaining nibbles and ID locations. The protected checksums in

Table 7-2 assume that the Insert Checksum in User ID Memory box is checked.

The checksum of a code-protected device is computed in the following manner: the Least Significant nibble of each user

ID is used to create a 16-bit value. The Least Significant nibble of user ID location 8000h is the Most Significant nibble

of the 16-bit value. The Least Significant nibble of user ID location 8001h is the second Most Significant nibble, and so

forth for the remaining user IDs and 16-bit value nibbles. The resulting 16-bit value is summed with the Configuration

Words. All unimplemented Configuration bits are masked to ‘0’.

TABLE 7-1:

CONFIGURATION WORD MASK VALUES

Part Variant

Config. Word 1 Mask

Config. Word 2 Mask

Config. Word 3 Mask

PIC12(L)F1612/16(L)F1613

0EE3h

3F83h

3F7Fh

PIC16(L)F1614/8

0EE3h

3F87h

3F7Fh

PIC16(L)F1615/9

3EE3h

3F87h

3F7Fh

TABLE 7-2:

CHECKSUMS

Device

Config1

Config2

Config3

Checksum

Unprotected Protected

Mask

Word

Mask

Word

Mask

Unprotected

Code-protected

Blank

00AAh

First

and Last

Blank

00AAh

First

and Last

PIC12F1612

3FFFh

3F7Fh

0EE3h 3FFFh 3F83h 3FFFh 3F7Fh

85E5h

073Bh

134Ah

94A0h

PIC16F1613

3FFFh

3F7Fh

0EE3h 3FFFh 3F83h 3FFFh 3F7Fh

85E5h

073Bh

134Ah

94A0h

PIC16F1614

3FFFh

3F7Fh

0EE3h 3FFFh 3F87h 3FFFh 3F7Fh 7DE9h

FF3Fh

0B4Eh

8CA4h

PIC16F1615

3FFFh

3F7Fh

3EE7h 3FFFh 3F87h 3FFFh 3F7Fh 9DEDh

1F43h

5B56h

DCACh

PIC16F1618

3FFFh

3F7Fh

0EE3h 3FFFh 3F87h 3FFFh 3F7Fh 7DE9h

FF3Fh

0B4Eh

8CA4h

PIC16F1619

3FFFh

3F7Fh

3EE7h 3FFFh 3F87h 3FFFh 3F7Fh 9DEDh

1F43h

5B56h

DCACh

PIC12LF1612

3FFFh

3F7Fh

0EE3h 3FFFh 3F83h 3FFFh 3F7Fh

85E5h

073Bh

134Ah

94A0h

PIC16LF1613

3FFFh

3F7Fh

0EE3h 3FFFh 3F83h 3FFFh 3F7Fh

85E5h

073Bh

134Ah

94A0h

PIC16LF1614

3FFFh

3F7Fh

0EE3h 3FFFh 3F87h 3FFFh 3F7Fh 7DE9h

FF3Fh

0B4Eh

8CA4h

PIC16LF1615

3FFFh

3F7Fh

3EE7h 3FFFh 3F87h 3FFFh 3F7Fh 9DEDh

1F43h

5B56h

DCACh

PIC16LF1618

3FFFh

3F7Fh

0EE3h 3FFFh 3F87h 3FFFh 3F7Fh 7DE9h

FF3Fh

0B4Eh

8CA4h

PIC16LF1619

3FFFh

3F7Fh

3EE7h 3FFFh 3F87h 3FFFh 3F7Fh 9DEDh

1F43h

5B56h

DCACh