S-record checksum calculator

srec-checksum.py

#!/usr/bin/env python

# usage: $ ./srec-checksum.py <s-record without checksum>

import sys

cad = sys.argv[1]
i = 2
checksum = 0
while i<len(cad):
    checksum = checksum + ord(cad[i:i+2].decode("hex"))
    i+=2

if (cad[0:2] == "S1"):
    out = "Data record, address 16 bits"
    address = cad[4:8]
elif (cad[0:2] == "S2"): 
    out = "Data record, address 24 bits"
    address = cad[4:10]
elif (cad[0:2] == "S3"):
    out = "Data record, address 32 bits"
    address = cad[4:12]
elif (cad[0:2] == "S9"):
    out = "Termination record, address 16 bits"
    address = cad[4:8]
elif (cad[0:2] == "S8"):
    out = "Termination record, address 24 bits"
    address = cad[4:10]
elif (cad[0:2] == "S9"):
    out = "Termination record, address 32 bits"
    address = cad[4:12]
elif (cad[0:2] == "S0"):
    out = "Header record"
    address = "0000"

print "[*] Record type: %s\taddress=0x%s"%(out, address)
print "[*] Checksum: %s\n[*] S-Record: %s"%(hex(checksum^0xff)[-2:].upper(), cad + hex(checksum^0xff)[-2:].upper())

There is a bug here.

Must replace ^0xff with ^0xff & 0xff. Check 'FFFF' input

corrected simplified version:

def moto_checksum(data):
    i = 2
    checksum = 0
    while i<len(data):
        checksum = checksum + ord(data[i:i+2].decode("hex"))
        i+=2

    return hex(checksum^0xff&0xff)[-2:].upper()

js version:

function motoChecksum(data) {
    let i = 2
    let checksum = 0
    while (i < data.length) {
        checksum = checksum + parseInt(data.slice(i, i+2), 16)
        i+=2
    }

    return ((checksum^0xff)&0xff).toString(16).toUpperCase().padStart(2, '0')
}

This snippet for python3:

import sys

def moto_checksum(data):
    i = 2
    checksum = 0
    while i<len(data):
        checksum = checksum + int.from_bytes(bytes.fromhex(data[i:i+2]), byteorder="little")
        i+=2

    return hex(checksum^0xff&0xff)[-2:].upper()
    
checksum = moto_checksum(sys.argv[1])
print("Checksum: {0}\n".format(checksum))