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Refin bluetech design how to#
Refin bluetech design code#

However in a real calculation, you reflect the polynomial instead, which takes care of both reflections.Ĭ) Yes, XorOut is the what you exclusive-or the final result with. The exclusive-or of Init is applied after the reflection, which you can verify using CRC-16/RIELLO in that table.Ī) RefIn has nothing to do with the padded bits. Reflect those bits and we get 0xc9cd, the expected result. Divide by 0x18005 and you get the remainder 0xb393. We start with the message with the bits in each byte reflected and the first 16 bits inverted. We now have what we need to compute CRC-16/MODBUS, which has both a non-zero Init value ( 0xffff) and RefIn and RefOut as true. That is what you see as the result in the table. Now we reflect all of those bits (not in each byte, but all 16 bits), and we get 0xd2cd. Dividing by the polynomial 0x18005 we get 0xb34b. The input message is then: 80 08 03 c0 00 80. RefOut means that we reflect the bits of the remainder. RefIn means that we reflect the bits in each byte of input. The next step is dealing with RefIn and RefOut being true. You will get what is in the table, 0xb53f. Now do what you know on that, but with the polynomial 0x11021. To compute the CRC-16/CCITT-FALSE on your data, you exclusive-or the first 16 bits of your data with the Init value of 0xffff. That one has an initial value that is not zero, but still has RefIn and RefOut as false, like CRC-16/BUYPASS.

Refin bluetech design how to#

You now know how to correctly calculate CRC-16/BUYPASS, so we'll start from there.

3rd applying RefOut for complete output/remainder (remainder maximum 16 bits in CRC16)ī) Referring to RefIn and RefOut: Is it always reflecting 8 bits for input and all bits for output nonetheless I use CRC8 or CRC16 or CRC32?Ĭ) What do the 3rd (check) and 8th (XorOut) column in the website I am referring to mean? The latter seems rather easy, I am guessing its apllied by computing the value xor after RefOut just like the InitValue?.

2nd xor InitValue with (in CRC16) for the first 16 bits.

1st applying RefIn for complete input (including padded bits).Not needed but appreciated.Ī) The order of computation would be. However, now that I can compute CRC16/Modbus there are some questions left for clearification. Thanks in advance.ĮDIT1: According to this site, "1st attempt" points to another CRC16-method with same polynomial but a different initial value (0x0000), which tells me, the calculation should be correct.ĮDIT2: Mark Adlers Answer does the trick.

Refin bluetech design code#

I honestly did spent many hours searching for an answer, but every explanation is based on code examples in C/C++ or others, which I don't understand. It would be great if someone could explain, or clarify my assumptions. What I don't know is how to incorporate the initial value - is it used to pad the data word with it instead of zeros? Or do I need to reverse the answer? Something else?ġst attempt: Padding by 16 bits with zeros.Ĭalculated remainder in binary would be 1111 1111 1001 1011 which is FF9B in hex and incorrect for CrC16/Modbus, but correct for CRC16/BypassĢnd attempt: Padding by 16 bits with ones, due to initial value.Ĭalculated remainder in binary would be 0000 0000 0110 0100 which is 0064 in hex and incorrect. I presume my transformation into binary is correct. I did calculate this manually like the example above, but I'd rather not write this down in binary in this question.

example message in hex: 01 10 C0 03 00 01.

Of course I would love to understand how different versions of CRCs work, but my main interest is to simply understand what mechanism is applied here. Searching for an answer I have seen a lot of different approaches with reversing, dependence on little or big endian, etc., which alter the outcome from the given 011.

calculation: 0100 1011 000 / 1001 -> remainder: 011Įdit1: So far verified by Mark Adler in previous comments/answers.

padded by 3 bits because of highest exponent x 3.

The following test example is supposed to check if my basic understanding is correct: I have learned that a basic CRC is a polynomial division of the data word, which is padded with zeros, depending on the length of the polynomial.

I am using the ModBus RTU, and I'm trying to figure out how to calculate the CRC16.