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Forum Index : Microcontroller and PC projects : (MM-DM) CRC-8 library or code sample
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| Greg Fordyce Senior Member  Joined: 16/09/2011 Location: United KingdomPosts: 153 |
I am wondering if anyone has a code snippet or library for doing CRC-8 error checking with the polynomial of X^8 + X^2 + X + 1. I briefly though I might be able to use the built in function OWCRC8() but it appears to use a different polynomial (X^8 + X^5 + X^4 + 1). 
I need to process data streams of up to 18 bytes plus the crc byte from a Linear Technology LTC6802-2 battery monitor. Just thought I would ask before I roll my own, no point reinventing the wheel if I don't have to.  |
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| Greg Fordyce Senior Member Joined: 16/09/2011 Location: United KingdomPosts: 153 |
I've found a very useful app note from Maxim, App note 3479. It describes a simple table based way of doing crc checking with the same poly that I need, and it even links to the 256 byte table. In the end its just a few lines of code. Here's what I've got so far. dim datastream(3),crctable(256) datastream(0) = 128 datastream(1) = 1 datastream(2) = 163 FOR i = 0 to 255 READ crctable(i) NEXT i crcregister = 0 FOR x = 0 to 3 crcregister = datastream(x) XOR crctable(crcregister) PRINT crcregister NEXT x DATA 0,7,14,9,28,27,18,21 DATA 56,63,54,49,36,35,42,45 DATA 112,119,126,121,108,107,98,101 DATA 72,79,70,65,84,83,90,93 DATA 224,231,238,233,252,251,242,245 DATA 216,223,214,209,196,195,202,205 DATA 144,151,158,153,140,139,130,133 DATA 168,175,166,161,180,179,186,189 DATA 199,192,201,206,219,220,213,210 DATA 255,248,241,246,227,228,237,234 DATA 183,176,185,190,171,172,165,162 DATA 143,136,129,134,147,148,157,154 DATA 39,32,41,46,59,60,53,50 DATA 31,24,17,22,3,4,13,10 DATA 87,80,89,94,75,76,69,66 DATA 111,104,97,102,115,116,125,122 DATA 137,142,135,128,149,146,155,156 DATA 177,182,191,184,173,170,163,164 DATA 249,254,247,240,229,226,235,236 DATA 193,198,207,200,221,218,211,212 DATA 105,110,103,96,117,114,123,124 DATA 81,86,95,88,77,74,67,68 DATA 25,30,23,16,5,2,11,12 DATA 33,38,47,40,61,58,51,52 DATA 78,73,64,71,82,85,92,91 DATA 118,113,120,127,106,109,100,99 DATA 62,57,48,55,34,37,44,43 DATA 6,1,8,15,26,29,20,19 DATA 174,169,160,167,178,181,188,187 DATA 150,145,152,159,138,141,132,131 DATA 222,217,208,215,194,197,204,203 DATA 230,225,232,239,250,253,244,243 In this code the sample data (datastream) is hard coded to the example given in the app note, obviously this needs to be changed to read actual data streams. There are 2 ways of using this. If you proess a data stream with the crc byte, the variable crcregister should = 0 if there are no errors. If you process a data stream without the crc byte, then crcregister will equal the crc byte to be appended on the end of the data stream. Greg P.S. I finally understand the point of the DOS version of MMBasic. I used it to figure out this code.  |
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