© 1996 Microchip Technology Inc.

DS30139I-page 9

EPROM Memory Programming Specification

4.3

CHECKSUM COMPUTATION

The checksum is calculated by summing the following:

• The contents of all program memory locations

• The configuration word, appropriately masked

• Masked ID locations (when applicable)

The least significant 16 bits of this sum is the check-

sum.

The following table describes how to calculate the

checksum for each device. Note that the checksum cal-

culation differs depending on the code protect setting.

Since the program memory locations read out differ-

ently depending on the code protect setting, the table

describes how to manipulate the actual program mem-

ory values to simulate the values that would be read

from a protected device. When calculating a checksum

by reading a device, the entire program memory can

simply be read and summed. The configuration word

and ID locations can always be read.

Note that some older devices have an additional value

added in the checksum. This is to maintain compatibil-

ity with older device programmer checksums.

TABLE 4-4:

CHECKSUM COMPUTATION

Device

Code

Protect

Checksum*

Blank

Value

0xC0DE at 0

and max

address

PIC17C42

MP mode

MC mode

EMC mode

PMC mode

SUM[0x000:0x7FF] + CFGW & 0x005F + 0xFFA0

SUM[0x000:0x7FF] + CFGW & 0x005F + 0xFFA0

SUM[0x000:0x7FF] + CFGW & 0x005F + 0xFFA0

SUM_XNOR8[0x000:0x7FF] + CFGW & 0x005F + 0xFFA0

0xF7FF

0xF7EF

0xF7BF

0xF7AF

0x79BD

0x79AD

0x797D

0xBB73

PIC17C42A

MP mode

MC mode

EMC mode

PMC mode

SUM[0x000:0x7FF] + CFGW & 0x015F

SUM[0x000:0x7FF] + CFGW & 0x015F

SUM[0x000:0x7FF] + CFGW & 0x015F

SUM_XNOR8[0x000:0x7FF] + CFGW & 0x015F

0xF95F

0xF94F

0xF91F

0xF80F

0x7B1D

0x7B0D

0x7ADD

0xBBD3

PIC17CR42

MP mode

MC mode

EMC mode

PMC mode

SUM[0x000:0x7FF] + CFGW & 0x015F

SUM[0x000:0x7FF] + CFGW & 0x015F

SUM[0x000:0x7FF] + CFGW & 0x015F

SUM_XNOR8[0x000:0x7FF] + CFGW & 0x015F

0xF95F

0xF94F

0xF91F

0xF80F

0x7B1D

0x7B0D

0x7ADD

0xBBD3

PIC17C43

MP mode

MC mode

EMC mode

PMC mode

SUM[0x000:0xFFF] + CFGW & 0x015F

SUM[0x000:0xFFF] + CFGW & 0x015F

SUM[0x000:0xFFF] + CFGW & 0x015F

SUM_XNOR8[0x000:0xFFF] + CFGW & 0x015F

0xF15F

0xF14F

0xF11F

0xF00F

0x731D

0x730D

0x72DD

0xB3D3

PIC17CR43

MP mode

MC mode

EMC mode

PMC mode

SUM[0x000:0xFFF] + CFGW & 0x015F

SUM[0x000:0xFFF] + CFGW & 0x015F

SUM[0x000:0xFFF] + CFGW & 0x015F

SUM_XNOR8[0x000:0xFFF] + CFGW & 0x015F

0xF15F

0xF14F

0xF11F

0xF00F

0x731D

0x730D

0x72DD

0xB3D3

PIC17C44

MP mode

MC mode

EMC mode

PMC mode

SUM[0x000:0x1FFF] + CFGW & 0x015F

SUM[0x000:0x1FFF] + CFGW & 0x015F

SUM[0x000:0x1FFF] + CFGW & 0x015F

SUM_XNOR8[0x000:0x1FFF] + CFGW & 0x015F

0xE15F

0xE14F

0xE11F

0xE00F

0x631D

0x630D

0x62DD

0xA3D3

Legend: CFGW = Configuration Word

SUM[a:b] = [Sum of locations a to b inclusive]

SUM_XNOR8(a:b) = [Sum of 8-bit wide XNOR copied into upper and lower byte, of locations a to b inclusive]

*Checksum = [Sum of all the individual expressions] MODULO [0xFFFF]

+ = Addition

& = Bitwise AND