php实现modbus CRC校验

一：计算CRC校验函数

function calculateCRC16Modbus($string)
{$crcBytes = [];for ($i = 0; $i < strlen($string); $i += 2) {$crcBytes[] = hexdec(substr($string, $i, 2));}$crc = 0xFFFF;$polynomial = 0xA001;  // This is the polynomial x^16 + x^15 + x^2 + 1foreach ($crcBytes as $byte) {$crc ^= $byte;for ($i = 0; $i < 8; $i++) {if ($crc & 0x0001) {$crc = (($crc >> 1) ^ $polynomial) & 0xFFFF;} else {$crc >>= 1;}}}return $crc;
}

二：调用CRC校验

$request = 'XXXXXXXX';
$res = calculateCRC16Modbus($request);
echo str_pad(strtoupper(dechex($res %256)), 2, "0", STR_PAD_LEFT);//低八位
echo str_pad(strtoupper(dechex(floor($res /256))), 2, "0", STR_PAD_LEFT);高八位