mb_crc.c

#include "modbus_conf.h"

#if MODBUS_USE_TABLE_CRC
static const uint16_t crc16Table[] = {
    0x0000, 0xC1C0, 0x81C1, 0x4001, 0x01C3, 0xC003, 0x8002, 0x41C2, 0x01C6, 0xC006, 0x8007, 0x41C7, 0x0005, 0xC1C5,
    0x81C4, 0x4004, 0x01CC, 0xC00C, 0x800D, 0x41CD, 0x000F, 0xC1CF, 0x81CE, 0x400E, 0x000A, 0xC1CA, 0x81CB, 0x400B,
    0x01C9, 0xC009, 0x8008, 0x41C8, 0x01D8, 0xC018, 0x8019, 0x41D9, 0x001B, 0xC1DB, 0x81DA, 0x401A, 0x001E, 0xC1DE,
    0x81DF, 0x401F, 0x01DD, 0xC01D, 0x801C, 0x41DC, 0x0014, 0xC1D4, 0x81D5, 0x4015, 0x01D7, 0xC017, 0x8016, 0x41D6,
    0x01D2, 0xC012, 0x8013, 0x41D3, 0x0011, 0xC1D1, 0x81D0, 0x4010, 0x01F0, 0xC030, 0x8031, 0x41F1, 0x0033, 0xC1F3,
    0x81F2, 0x4032, 0x0036, 0xC1F6, 0x81F7, 0x4037, 0x01F5, 0xC035, 0x8034, 0x41F4, 0x003C, 0xC1FC, 0x81FD, 0x403D,
    0x01FF, 0xC03F, 0x803E, 0x41FE, 0x01FA, 0xC03A, 0x803B, 0x41FB, 0x0039, 0xC1F9, 0x81F8, 0x4038, 0x0028, 0xC1E8,
    0x81E9, 0x4029, 0x01EB, 0xC02B, 0x802A, 0x41EA, 0x01EE, 0xC02E, 0x802F, 0x41EF, 0x002D, 0xC1ED, 0x81EC, 0x402C,
    0x01E4, 0xC024, 0x8025, 0x41E5, 0x0027, 0xC1E7, 0x81E6, 0x4026, 0x0022, 0xC1E2, 0x81E3, 0x4023, 0x01E1, 0xC021,
    0x8020, 0x41E0, 0x01A0, 0xC060, 0x8061, 0x41A1, 0x0063, 0xC1A3, 0x81A2, 0x4062, 0x0066, 0xC1A6, 0x81A7, 0x4067,
    0x01A5, 0xC065, 0x8064, 0x41A4, 0x006C, 0xC1AC, 0x81AD, 0x406D, 0x01AF, 0xC06F, 0x806E, 0x41AE, 0x01AA, 0xC06A,
    0x806B, 0x41AB, 0x0069, 0xC1A9, 0x81A8, 0x4068, 0x0078, 0xC1B8, 0x81B9, 0x4079, 0x01BB, 0xC07B, 0x807A, 0x41BA,
    0x01BE, 0xC07E, 0x807F, 0x41BF, 0x007D, 0xC1BD, 0x81BC, 0x407C, 0x01B4, 0xC074, 0x8075, 0x41B5, 0x0077, 0xC1B7,
    0x81B6, 0x4076, 0x0072, 0xC1B2, 0x81B3, 0x4073, 0x01B1, 0xC071, 0x8070, 0x41B0, 0x0050, 0xC190, 0x8191, 0x4051,
    0x0193, 0xC053, 0x8052, 0x4192, 0x0196, 0xC056, 0x8057, 0x4197, 0x0055, 0xC195, 0x8194, 0x4054, 0x019C, 0xC05C,
    0x805D, 0x419D, 0x005F, 0xC19F, 0x819E, 0x405E, 0x005A, 0xC19A, 0x819B, 0x405B, 0x0199, 0xC059, 0x8058, 0x4198,
    0x0188, 0xC048, 0x8049, 0x4189, 0x004B, 0xC18B, 0x818A, 0x404A, 0x004E, 0xC18E, 0x818F, 0x404F, 0x018D, 0xC04D,
    0x804C, 0x418C, 0x0044, 0xC184, 0x8185, 0x4045, 0x0187, 0xC047, 0x8046, 0x4186, 0x0182, 0xC042, 0x8043, 0x4183,
    0x0041, 0xC181, 0x8180, 0x4040
};

uint16_t MBRTU_CRC(uint8_t *buf, uint16_t len)
{
    uint16_t i;
    uint16_t crc = 0xFFFF;

    for (i = 0; i < len; i++)
    {
        crc = (uint16_t) ((crc << 8) ^ crc16Table[(crc >> 8) ^ buf[i]]);
    }

    return crc;
}

#else
uint16_t MBRTU_CRC(uint8_t *buf, uint16_t len)
{
    uint16_t crc = 0xFFFF;
    uint16_t pos;
    uint8_t i;

    for (pos = 0; pos < len; pos++)
    {
        crc ^= (uint16_t) buf[pos];

        for (i = 8; i > 0; i--)
        {
            if ((crc & 0x0001) != 0)
            {
                crc >>= 1;
                crc ^= 0xA001;
            }
            else
            {
                crc >>= 1;
            }
        }
    }

    return (uint16_t) (((crc << 8) & 0xff00) | ((crc >> 8) & 0xff));
}

#endif /* MODBUS_USE_TABLE_CRC */