PIC16LF145X Datasheet, PDF(28/38 Page) Microchip Technology – PIC16(L)F145X Memory Programming Specification

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PIC16LF145X Datasheet, PDF (28/38 Pages) Microchip Technology – PIC16(L)F145X Memory Programming Specification

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PIC16(L)F145X

7.3 Checksum Computation

The checksum is calculated by two different methods

dependent on the setting of the CP Configuration bit.

TABLE 7-1: CONFIGURATION WORD

MASK VALUES

Device

Config. Word 1 Config. Word 2

Mask

PIC16(L)F1454

PIC16(L)F1455

PIC16(L)F1459

3EFFh

3FF3h

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 â0â.

EXAMPLE 7-1:

CHECKSUM COMPUTED WITH PROGRAM CODE PROTECTION DISABLED

(CP = 1), PIC16F1459, BLANK DEVICE

PIC16F1459

Sum of Memory addresses 0000h-1FFFh

E000h(1)

Configuration Word 1

3FFFh(2)

Configuration Word 1 mask

3EFFh(3)

Configuration Word 2

3FFFh(4)

Configuration Word 2 mask

3FF3h(5)

Checksum

= E000h + (3FFFh and 3EFFh) + (3FFFh and 3FF3h)(6)

= E000h + 3EFFh + 3FF3h

= 5EF2h

Note 1:

This value is obtained by taking the total number of program memory locations (0x000 to 0x1FFFh

which is E000h) and multiplying it by the blank memory value of 0x3FFF to get the sum of 1FF F800h.

Then, truncate to 16 bits, thus having a final value of F800h.

This value is obtained by making all bits of the Configuration Word 1 a â1â, then converting it to hex, thus

having a value of 3FFFh.

This value is obtained by making all used bits of the Configuration Word 1 a â1â, then converting it to hex,

thus having a value of 3EFFh.

This value is obtained by making all bits of the Configuration Word 2 a â1â, then converting it to hex, thus

having a value of 3FFFh.

This value is obtained by making all used bits of the Configuration Word 2 a â1â, then converting it to hex,

thus having a value of 3FF3h.

This value is obtained by ANDing the Configuration Word value with the Configuration Word Mask Value

and adding it to the sum of memory addresses: (3FFFh and 3EFFh) + (3FFFh and 3FF3h) + E000h =

1 34FEh. Then, truncate to 16 bits, thus having a final value of 5EF2h.

DS41620C-page 28

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