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UART CRC Check
Posted: Wed Sep 05, 2018 7:55 am
by Lord Grezington
Hello Everyone...
I have this project where I am trying to communicate with an IC that has a difficult CRC check. Anyone have any idea how I would implement this with Flowcode?
Thanks
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Re: UART CRC Check
Posted: Thu Sep 06, 2018 1:47 pm
by Benj
Hello,
Yes that should be fine.
First create a byte variable named CRC and initialise it to 0.
Next create a loop icon that will run 8 times, you need to run this loop for every byte you send or receive so it might make sense to put the loop in a macro you can call when sending or receiving bytes. Next create a variable named data you might want to make it local to the macro if you created one.
You can simply do the following using a decision and calculation icons inside the loop. Remember to load the .Data variable with the byte value that's been received or ready to transmit before the loop.
Code: Select all
Decision: (CRC >> 7) ^ (.Data & 0x01)
Yes: Calculation: CRC = (CRC << 1) ^ 0x07
No: Calculation: CRC = (CRC << 1)
Calculation: .Data = .Data >> 1
Re: UART CRC Check
Posted: Wed Sep 12, 2018 9:41 am
by Lord Grezington
Hi Ben
Works great, thanks again...
Re: UART CRC Check
Posted: Mon Nov 05, 2018 7:49 pm
by Brendan
As I use CRCs with Flowcode a lot (particularly Maxim 1-wire, etc), and assuming you've got 256 Bytes of program memory to spare for an 8-bit CRC, I'd like to chip in with a popular alternative of pasting a 256-byte table (relevant to your CRC polynomial) to the Flowcode LUT component.
Such CRC tables may be published by manufacturers in application notes, or can be found on the internet - though always wise to test/debug with an arbitrary Byte string and see if your result concurs with an online calculator.
The primary benefit to this approach is speed, particularly when streaming out/in indeterminate amounts of data with limited PIC speed...
CurrentCRC XOR DataByte = LUTindex, the returned Byte from that location being the new CRC.
Such an approach also applies to 16-bit CRCs and higher, with code space trade-off and appropriate Byte-shifting, but where speed gain becomes even more noticeable.
All the best,
Brendan