Find out CRC or CHECKSUM of RS232 data

Question

I need to communicate with a RS232 device, I have no specs or information available.

I send a 16 byte command and get a 16 byte result back. The last byte looks like some kind of crc or checksum, I have tried using this http://miscel.dk/MiscEl/miscelCRCandChecksum.html with no luck.

Anyone can reverse engineer the crc/checksum algorithm? here is some data captured with an RS-232 monitor program:

01 80 42 00 00 00 00 00 00 00 00 00 00 00 01 B3
01 80 42 00 00 00 00 00 00 00 00 00 00 00 02 51
01 80 42 00 00 00 00 00 00 00 00 00 00 00 03 0F
01 80 42 00 00 00 00 00 00 00 00 00 00 00 04 8C
01 80 42 00 00 00 00 00 00 00 00 00 00 00 05 D2
01 80 42 00 00 00 00 00 00 00 00 00 00 00 06 30
01 80 42 00 00 00 00 00 00 00 00 00 00 00 07 6E
01 80 42 00 00 00 00 00 00 00 00 00 00 00 08 2F
01 80 42 00 00 00 00 00 00 00 00 00 00 00 09 71
01 80 42 00 00 00 00 00 00 00 00 00 00 00 0A 93
01 80 42 00 00 00 00 00 00 00 00 00 00 00 0B CD
01 80 42 00 00 00 00 00 00 00 00 00 00 00 0C 4E
01 80 42 00 00 00 00 00 00 00 00 00 00 00 0D 10
01 80 42 00 00 00 00 00 00 00 00 00 00 00 0E F2
01 80 42 00 00 00 00 00 00 00 00 00 00 00 0F AC
01 80 42 00 00 00 00 00 00 00 00 00 00 00 10 70
01 80 42 00 00 00 00 00 00 00 00 00 00 00 11 2E
01 80 42 00 00 00 00 00 00 00 00 00 00 00 12 CC
01 80 42 00 00 00 00 00 00 00 00 00 00 00 13 92
01 80 42 00 00 00 00 00 00 00 00 00 00 00 14 11
01 80 42 00 00 00 00 00 00 00 00 00 00 00 15 4F
01 80 42 00 00 00 00 00 00 00 00 00 00 00 16 AD
01 80 42 00 00 00 00 00 00 00 00 00 00 00 17 F3
01 80 42 00 00 00 00 00 00 00 00 00 00 00 18 B2
01 80 42 00 00 00 00 00 00 00 00 00 00 00 19 EC
01 80 42 00 00 00 00 00 00 00 00 00 00 00 1A 0E
01 80 42 00 00 00 00 00 00 00 00 00 00 00 1B 50
01 80 42 00 00 00 00 00 00 00 00 00 00 00 1C D3
01 80 42 00 00 00 00 00 00 00 00 00 00 00 1D 8D
01 80 42 00 00 00 00 00 00 00 00 00 00 00 1E 6F
01 80 42 00 00 00 00 00 00 00 00 00 00 00 1F 31
01 80 42 00 00 00 00 00 00 00 00 00 00 00 20 CE
01 80 42 00 00 00 00 00 00 00 00 00 00 00 21 90
01 80 42 00 00 00 00 00 00 00 00 00 00 00 22 72
01 80 42 00 00 00 00 00 00 00 00 00 00 00 23 2C
01 80 42 00 00 00 00 00 00 00 00 00 00 00 24 AF
01 80 42 00 00 00 00 00 00 00 00 00 00 00 25 F1
01 80 42 00 00 00 00 00 00 00 00 00 00 00 26 13
01 80 42 00 00 00 00 00 00 00 00 00 00 00 27 4D
01 80 42 00 00 00 00 00 00 00 00 00 00 00 28 0C
01 80 42 00 00 00 00 00 00 00 00 00 00 00 29 52
01 80 42 00 00 00 00 00 00 00 00 00 00 00 2A B0
01 80 42 00 00 00 00 00 00 00 00 00 00 00 2B EE
01 80 42 00 00 00 00 00 00 00 00 00 00 00 2C 6D
01 80 42 00 00 00 00 00 00 00 00 00 00 00 2D 33
01 80 42 00 00 00 00 00 00 00 00 00 00 00 2E D1
01 80 42 00 00 00 00 00 00 00 00 00 00 00 2F 8F
01 80 42 00 00 00 00 00 00 00 00 00 00 00 30 53
01 80 42 00 00 00 00 00 00 00 00 00 00 00 31 0D
01 80 42 00 00 00 00 00 00 00 00 00 00 00 32 EF
01 80 42 00 00 00 00 00 00 00 00 00 00 00 33 B1
01 80 42 00 00 00 00 00 00 00 00 00 00 00 34 32
01 80 42 00 00 00 00 00 00 00 00 00 00 00 35 6C
01 80 42 00 00 00 00 00 00 00 00 00 00 00 36 8E
01 80 42 00 00 00 00 00 00 00 00 00 00 00 37 D0
01 80 42 00 00 00 00 00 00 00 00 00 00 00 38 91
01 80 42 00 00 00 00 00 00 00 00 00 00 00 39 CF
01 80 42 00 00 00 00 00 00 00 00 00 00 00 3A 2D
01 80 42 00 00 00 00 00 00 00 00 00 00 00 3B 73
01 80 42 00 00 00 00 00 00 00 00 00 00 00 3C F0
01 80 42 00 00 00 00 00 00 00 00 00 00 00 3D AE
01 80 42 00 00 00 00 00 00 00 00 00 00 00 3E 4C
01 80 42 00 00 00 00 00 00 00 00 00 00 00 3F 12
01 80 42 00 00 00 00 00 00 00 00 00 00 00 40 AB
01 80 42 00 00 00 00 00 00 00 00 00 00 00 41 F5
01 80 42 00 00 00 00 00 00 00 00 00 00 00 42 17
01 80 42 00 00 00 00 00 00 00 00 00 00 00 43 49
01 80 42 00 00 00 00 00 00 00 00 00 00 00 44 CA
01 80 42 00 00 00 00 00 00 00 00 00 00 00 45 94
01 80 42 00 00 00 00 00 00 00 00 00 00 00 46 76
01 80 42 00 00 00 00 00 00 00 00 00 00 00 47 28
01 80 42 00 00 00 00 00 00 00 00 00 00 00 48 69
01 80 42 00 00 00 00 00 00 00 00 00 00 00 49 37
01 80 42 00 00 00 00 00 00 00 00 00 00 00 4A D5
01 80 42 00 00 00 00 00 00 00 00 00 00 00 4B 8B
01 80 42 00 00 00 00 00 00 00 00 00 00 00 4C 08
01 80 42 00 00 00 00 00 00 00 00 00 00 00 4D 56
01 80 42 00 00 00 00 00 00 00 00 00 00 00 4E B4
01 80 42 00 00 00 00 00 00 00 00 00 00 00 4F EA
01 80 42 00 00 00 00 00 00 00 00 00 00 00 50 36
01 80 42 00 00 00 00 00 00 00 00 00 00 00 51 68
01 80 42 00 00 00 00 00 00 00 00 00 00 00 52 8A
01 80 42 00 00 00 00 00 00 00 00 00 00 00 53 D4
01 80 42 00 00 00 00 00 00 00 00 00 00 00 54 57
01 80 42 00 00 00 00 00 00 00 00 00 00 00 55 09
01 80 42 00 00 00 00 00 00 00 00 00 00 00 56 EB
01 80 42 00 00 00 00 00 00 00 00 00 00 00 57 B5
01 80 42 00 00 00 00 00 00 00 00 00 00 00 58 F4
01 80 42 00 00 00 00 00 00 00 00 00 00 00 59 AA
01 80 42 00 00 00 00 00 00 00 00 00 00 00 5A 48
01 80 42 00 00 00 00 00 00 00 00 00 00 00 5B 16
01 80 42 00 00 00 00 00 00 00 00 00 00 00 5C 95
01 80 42 00 00 00 00 00 00 00 00 00 00 00 5D CB
01 80 42 00 00 00 00 00 00 00 00 00 00 00 5E 29
01 80 42 00 00 00 00 00 00 00 00 00 00 00 5F 77
01 80 42 00 00 00 00 00 00 00 00 00 00 00 60 88
01 80 42 00 00 00 00 00 00 00 00 00 00 00 61 D6
01 80 42 00 00 00 00 00 00 00 00 00 00 00 62 34
01 80 42 00 00 00 00 00 00 00 00 00 00 00 63 6A
01 80 42 00 00 00 00 00 00 00 00 00 00 00 64 E9
01 80 42 00 00 00 00 00 00 00 00 00 00 00 65 B7
01 80 42 00 00 00 00 00 00 00 00 00 00 00 66 55
01 80 42 00 00 00 00 00 00 00 00 00 00 00 67 0B
01 80 42 00 00 00 00 00 00 00 00 00 00 00 68 4A
01 80 42 00 00 00 00 00 00 00 00 00 00 00 69 14
01 80 42 00 00 00 00 00 00 00 00 00 00 00 6A F6
01 80 42 00 00 00 00 00 00 00 00 00 00 00 6B A8
01 80 42 00 00 00 00 00 00 00 00 00 00 00 6C 2B
01 80 42 00 00 00 00 00 00 00 00 00 00 00 6D 75
01 80 42 00 00 00 00 00 00 00 00 00 00 00 6E 97
01 80 42 00 00 00 00 00 00 00 00 00 00 00 6F C9
01 80 42 00 00 00 00 00 00 00 00 00 00 00 70 15
01 80 42 00 00 00 00 00 00 00 00 00 00 00 71 4B
01 80 42 00 00 00 00 00 00 00 00 00 00 00 72 A9
01 80 42 00 00 00 00 00 00 00 00 00 00 00 73 F7
01 80 42 00 00 00 00 00 00 00 00 00 00 00 74 74
01 80 42 00 00 00 00 00 00 00 00 00 00 00 75 2A
01 80 42 00 00 00 00 00 00 00 00 00 00 00 76 C8
01 80 42 00 00 00 00 00 00 00 00 00 00 00 77 96
01 80 42 00 00 00 00 00 00 00 00 00 00 00 78 D7
01 80 42 00 00 00 00 00 00 00 00 00 00 00 79 89
01 80 42 00 00 00 00 00 00 00 00 00 00 00 7A 6B
01 80 42 00 00 00 00 00 00 00 00 00 00 00 7B 35
01 80 42 00 00 00 00 00 00 00 00 00 00 00 7C B6
01 80 42 00 00 00 00 00 00 00 00 00 00 00 7D E8
01 80 42 00 00 00 00 00 00 00 00 00 00 00 7E 0A
01 80 42 00 00 00 00 00 00 00 00 00 00 00 7F 54
01 80 42 00 00 00 00 00 00 00 00 00 00 00 80 61
01 80 42 00 00 00 00 00 00 00 00 00 00 00 81 3F
01 80 42 00 00 00 00 00 00 00 00 00 00 00 82 DD
01 80 42 00 00 00 00 00 00 00 00 00 00 00 83 83
01 80 42 00 00 00 00 00 00 00 00 00 00 00 84 00
01 80 42 00 00 00 00 00 00 00 00 00 00 00 85 5E
01 80 42 00 00 00 00 00 00 00 00 00 00 00 86 BC
01 80 42 00 00 00 00 00 00 00 00 00 00 00 87 E2
01 80 42 00 00 00 00 00 00 00 00 00 00 00 88 A3
01 80 42 00 00 00 00 00 00 00 00 00 00 00 89 FD
01 80 42 00 00 00 00 00 00 00 00 00 00 00 8A 1F
01 80 42 00 00 00 00 00 00 00 00 00 00 00 8B 41
01 80 42 00 00 00 00 00 00 00 00 00 00 00 8C C2
01 80 42 00 00 00 00 00 00 00 00 00 00 00 8D 9C
01 80 42 00 00 00 00 00 00 00 00 00 00 00 8E 7E
01 80 42 00 00 00 00 00 00 00 00 00 00 00 8F 20
01 80 42 00 00 00 00 00 00 00 00 00 00 00 90 FC
01 80 42 00 00 00 00 00 00 00 00 00 00 00 91 A2
01 80 42 00 00 00 00 00 00 00 00 00 00 00 92 40
01 80 42 00 00 00 00 00 00 00 00 00 00 00 93 1E
01 80 42 00 00 00 00 00 00 00 00 00 00 00 94 9D
01 80 42 00 00 00 00 00 00 00 00 00 00 00 95 C3
01 80 42 00 00 00 00 00 00 00 00 00 00 00 96 21
01 80 42 00 00 00 00 00 00 00 00 00 00 00 97 7F
01 80 42 00 00 00 00 00 00 00 00 00 00 00 98 3E
01 80 42 00 00 00 00 00 00 00 00 00 00 00 99 60
01 80 42 00 00 00 00 00 00 00 00 00 00 00 9A 82
01 80 42 00 00 00 00 00 00 00 00 00 00 00 9B DC
01 80 42 00 00 00 00 00 00 00 00 00 00 00 9C 5F
01 80 42 00 00 00 00 00 00 00 00 00 00 00 9D 01
01 80 42 00 00 00 00 00 00 00 00 00 00 00 9E E3
01 80 42 00 00 00 00 00 00 00 00 00 00 00 9F BD
01 80 42 00 00 00 00 00 00 00 00 00 00 00 A0 42
01 80 42 00 00 00 00 00 00 00 00 00 00 00 A1 1C
01 80 42 00 00 00 00 00 00 00 00 00 00 00 A2 FE
01 80 42 00 00 00 00 00 00 00 00 00 00 00 A3 A0
01 80 42 00 00 00 00 00 00 00 00 00 00 00 A4 23
01 80 42 00 00 00 00 00 00 00 00 00 00 00 A5 7D
01 80 42 00 00 00 00 00 00 00 00 00 00 00 A6 9F
01 80 42 00 00 00 00 00 00 00 00 00 00 00 A7 C1
01 80 42 00 00 00 00 00 00 00 00 00 00 00 A8 80
01 80 42 00 00 00 00 00 00 00 00 00 00 00 A9 DE
01 80 42 00 00 00 00 00 00 00 00 00 00 00 AA 3C
01 80 42 00 00 00 00 00 00 00 00 00 00 00 AB 62
01 80 42 00 00 00 00 00 00 00 00 00 00 00 AC E1
01 80 42 00 00 00 00 00 00 00 00 00 00 00 AD BF
01 80 42 00 00 00 00 00 00 00 00 00 00 00 AE 5D
01 80 42 00 00 00 00 00 00 00 00 00 00 00 AF 03
01 80 42 00 00 00 00 00 00 00 00 00 00 00 B0 DF
01 80 42 00 00 00 00 00 00 00 00 00 00 00 B1 81
01 80 42 00 00 00 00 00 00 00 00 00 00 00 B2 63
01 80 42 00 00 00 00 00 00 00 00 00 00 00 B3 3D
01 80 42 00 00 00 00 00 00 00 00 00 00 00 B4 BE
01 80 42 00 00 00 00 00 00 00 00 00 00 00 B5 E0
01 80 42 00 00 00 00 00 00 00 00 00 00 00 B6 02
01 80 42 00 00 00 00 00 00 00 00 00 00 00 B7 5C
01 80 42 00 00 00 00 00 00 00 00 00 00 00 B8 1D
01 80 42 00 00 00 00 00 00 00 00 00 00 00 B9 43
01 80 42 00 00 00 00 00 00 00 00 00 00 00 BA A1
01 80 42 00 00 00 00 00 00 00 00 00 00 00 BB FF
01 80 42 00 00 00 00 00 00 00 00 00 00 00 BC 7C
01 80 42 00 00 00 00 00 00 00 00 00 00 00 BD 22
01 80 42 00 00 00 00 00 00 00 00 00 00 00 BE C0
01 80 42 00 00 00 00 00 00 00 00 00 00 00 BF 9E
01 80 42 00 00 00 00 00 00 00 00 00 00 00 C0 27
01 80 42 00 00 00 00 00 00 00 00 00 00 00 C1 79
01 80 42 00 00 00 00 00 00 00 00 00 00 00 C2 9B
01 80 42 00 00 00 00 00 00 00 00 00 00 00 C3 C5
01 80 42 00 00 00 00 00 00 00 00 00 00 00 C4 46
01 80 42 00 00 00 00 00 00 00 00 00 00 00 C5 18
01 80 42 00 00 00 00 00 00 00 00 00 00 00 C6 FA
01 80 42 00 00 00 00 00 00 00 00 00 00 00 C7 A4
01 80 42 00 00 00 00 00 00 00 00 00 00 00 C8 E5
01 80 42 00 00 00 00 00 00 00 00 00 00 00 C9 BB
01 80 42 00 00 00 00 00 00 00 00 00 00 00 CA 59
01 80 42 00 00 00 00 00 00 00 00 00 00 00 CB 07
01 80 42 00 00 00 00 00 00 00 00 00 00 00 CC 84
01 80 42 00 00 00 00 00 00 00 00 00 00 00 CD DA
01 80 42 00 00 00 00 00 00 00 00 00 00 00 CE 38
01 80 42 00 00 00 00 00 00 00 00 00 00 00 CF 66
01 80 42 00 00 00 00 00 00 00 00 00 00 00 D0 BA
01 80 42 00 00 00 00 00 00 00 00 00 00 00 D1 E4
01 80 42 00 00 00 00 00 00 00 00 00 00 00 D2 06
01 80 42 00 00 00 00 00 00 00 00 00 00 00 D3 58
01 80 42 00 00 00 00 00 00 00 00 00 00 00 D4 DB
01 80 42 00 00 00 00 00 00 00 00 00 00 00 D5 85
01 80 42 00 00 00 00 00 00 00 00 00 00 00 D6 67
01 80 42 00 00 00 00 00 00 00 00 00 00 00 D7 39
01 80 42 00 00 00 00 00 00 00 00 00 00 00 D8 78
01 80 42 00 00 00 00 00 00 00 00 00 00 00 D9 26
01 80 42 00 00 00 00 00 00 00 00 00 00 00 DA C4
01 80 42 00 00 00 00 00 00 00 00 00 00 00 DB 9A
01 80 42 00 00 00 00 00 00 00 00 00 00 00 DC 19
01 80 42 00 00 00 00 00 00 00 00 00 00 00 DD 47
01 80 42 00 00 00 00 00 00 00 00 00 00 00 DE A5
01 80 42 00 00 00 00 00 00 00 00 00 00 00 DF FB
01 80 42 00 00 00 00 00 00 00 00 00 00 00 E0 04
01 80 42 00 00 00 00 00 00 00 00 00 00 00 E1 5A
01 80 42 00 00 00 00 00 00 00 00 00 00 00 E2 B8
01 80 42 00 00 00 00 00 00 00 00 00 00 00 E3 E6
01 80 42 00 00 00 00 00 00 00 00 00 00 00 E4 65
01 80 42 00 00 00 00 00 00 00 00 00 00 00 E5 3B
01 80 42 00 00 00 00 00 00 00 00 00 00 00 E6 D9
01 80 42 00 00 00 00 00 00 00 00 00 00 00 E7 87
01 80 42 00 00 00 00 00 00 00 00 00 00 00 E8 C6
01 80 42 00 00 00 00 00 00 00 00 00 00 00 E9 98
01 80 42 00 00 00 00 00 00 00 00 00 00 00 EA 7A
01 80 42 00 00 00 00 00 00 00 00 00 00 00 EB 24
01 80 42 00 00 00 00 00 00 00 00 00 00 00 EC A7
01 80 42 00 00 00 00 00 00 00 00 00 00 00 ED F9
01 80 42 00 00 00 00 00 00 00 00 00 00 00 EE 1B
01 80 42 00 00 00 00 00 00 00 00 00 00 00 EF 45
01 80 42 00 00 00 00 00 00 00 00 00 00 00 F0 99
01 80 42 00 00 00 00 00 00 00 00 00 00 00 F1 C7
01 80 42 00 00 00 00 00 00 00 00 00 00 00 F2 25
01 80 42 00 00 00 00 00 00 00 00 00 00 00 F3 7B
01 80 42 00 00 00 00 00 00 00 00 00 00 00 F4 F8
01 80 42 00 00 00 00 00 00 00 00 00 00 00 F5 A6
01 80 42 00 00 00 00 00 00 00 00 00 00 00 F6 44
01 80 42 00 00 00 00 00 00 00 00 00 00 00 F7 1A
01 80 42 00 00 00 00 00 00 00 00 00 00 00 F8 5B
01 80 42 00 00 00 00 00 00 00 00 00 00 00 F9 05
01 80 42 00 00 00 00 00 00 00 00 00 00 00 FA E7
01 80 42 00 00 00 00 00 00 00 00 00 00 00 FB B9
01 80 42 00 00 00 00 00 00 00 00 00 00 00 FC 3A
01 80 42 00 00 00 00 00 00 00 00 00 00 00 FD 64
01 80 42 00 00 00 00 00 00 00 00 00 00 00 FE 86
01 80 42 00 00 00 00 00 00 00 00 00 00 00 FF D8

The second to last byte seems to be a sequential number that starts over at 00 when it reaches FF. I have included the whole range from 00 to FF to make it easier to guess the crc/checksum method.

Cant add a comment, so I will add info here:

The last byte is the same when all the preceding 15 bytes are equal. This is the device: http://www.intelektron.com/productos/tya_rei4000.htm

CORRECTION (And I think I found a bug in the software) The device itself starts over at 00 after reaching FF in the second to last byte, but the software that sends commands to the device starts over at 01 when it reaches FF. Anyway I think this second to last sequence byte is not relevant to the crc/checksum problem.

CLARIFICATION The listed data are commands sent by the software, the replies by the device are not listed. The device responds to each of the above commands sending one row of stored data like:

80 01 C2 80 85 01 25 65 57 37 19 32 01 04 76 17

This line contains a 4 byte card number, a time and date, etc, not relevant I think to the crc/checksum problem.

ADDITIONAL INFO:

I have been poking around the VB6 ocxs of the software and got this:

Object: clsCRC8
Object: basComunicaciones2
Private sub Proc_1_0_30305330
  loc_30305352: var_8 = 30301198h
  loc_30305373: call basComunicaciones2.SetPropA(edi, arg_8, ebx)
  loc_30305376: var_4 = 0
End Sub

Private sub Proc_1_1_303053A0
  loc_303053C2: var_8 = 303011A0h
  loc_303053E2: call MSVBVM60.DLL.__vbaBoolVarNull(basComunicaciones2.Caption = %x1, arg_8, ebx)
  loc_303053EB: If MSVBVM60.DLL.__vbaBoolVarNull(basComunicaciones2.Caption <> %x1 <>  arg_8 Then GoTo loc_303054B8
  loc_303053F7: var_24 = FFFFFFFFh
  loc_303053FE: var_2C = 11
  loc_30305405: ecx = True
  loc_3030540D: call MSVBVM60.DLL.__vbaUI1I2
  loc_3030541C: edx = edx - 0001h
  loc_30305429: If edx-0001h < 0 Then GoTo loc_30305499
  loc_3030542B: 
  loc_30305443: di = di - basComunicaciones2.%x1 = GetIDsOfNames(%x2) 'Ignore this
  loc_30305447: If di < Me.GetTypeInfo Then GoTo loc_3030544F
  loc_30305449: Err.Raise
  loc_3030544F: 
  loc_30305451: GoTo loc_30305459
  loc_30305453: Err.Raise
  loc_30305459: 
  loc_3030546B: eax = "" And 000000FFh
  loc_30305478: If ecx+eax xor eax < 257 Then GoTo loc_30305480
  loc_3030547A: Err.Raise
  loc_30305480: 
  loc_30305492: var_18 = Var_Ret_1
  loc_30305495: If edi <= Me = %x1 Then GoTo loc_3030542B
  loc_30305499: 
  loc_3030549F: not al
  loc_303054A1: var_18 = Var_Ret_1
  loc_303054A4: var_24 = 0
  loc_303054AB: var_2C = 11
  loc_303054B2: ecx =
  loc_303054B8: 
  loc_303054DC: Exit Sub
End Sub

Private sub Proc_1_2_30306410
  loc_30306432: var_8 = 303011A8h
  loc_3030644F: var_38 = &H4011
  loc_30306489: If Len(Hex()) >= 2 Then GoTo loc_303064A1
  loc_3030649F: var_18 = 808463756 & var_18
  loc_303064A1: 
  loc_303064A6: GoTo loc_303064C1
  loc_303064C0: Exit Sub
  loc_303064C1: 
End Sub

I am pretty shure this calculates the CRC8 of the data:

Method Calcular(Paquete As , CantidadDeBytes As Integer) As Unsigned Small Integer Member of vbpComunicaciones2 (cached).clsCRC8 Defined in interface _clsCRC8

Anyone can get some sense out of this? sadly, I can´t.

Answer 1

The answer was here: http://blog.sina.com.cn/s/blog_5a1d5bca0100bjvx.html

0xff - result from algorithm from above link and everything matches up. Took me 2 afternoons and the help I got here, but finally nailed it.

Of course I more or less understand what that code is doing thanks to the link posted by Gerhard. Thank you.

Answer 2

It is not a checksum or data XOR.
There are a few CRC options that you can try. The data you give does not give a positive result on any easy crc solutions.

Commmon 8 bit CRC are:
Name : poly : normal / reversed / reverse of reciprocal
CRC-8-CCITT : 0x8 + x2 + x + 1 : 0x07 / 0xE0 / 0x83
CRC-8-Dallas/Maxim (1-Wire bus) : x8 + x5 + x4 + 1 : 0x31 / 0x8C / 0x98
CRC-8 : x8 + x7 + x6 + x4 + x2 + 1 : 0xD5 / 0xAB / 0xEA
CRC-8-SAE : x8 + x4 + x3 + x2 + 1 : 0x1D / 0xB8 / 0x8E
CRC-8-WCDMA : x8 + x7 + x4 + x3 + x + 1 0x9B / 0xD9 / 0xCD

Implementation options to mix it up would be:
Normal or reverse data bytes, Initial value(0xff or 0x00), Final XOR on not and reverse CRC result before Final XOR.

For a CRC it must be on of these option unless they rolled their own.

To learn more A Painless Guide to CRC Error Detection Algorithms.