swift 

let data = NSString(string : "ca 20 fe c1 04 03 03 07 01 ac")

    let dataArr = data.componentsSeparatedByString(" ")

    var bytes : [UInt8] = []

    for item in dataArr {

        let byte = UInt8(item, radix: 16)

        bytes.append(byte!);

    }

    let hexData = NSData(bytes: bytes, length: 10)

oc

NSString *strData = @"ca 20 fe c1 04 03 03 07 00 ac";

NSArray<NSString *> *dataArr = [strData componentsSeparatedByString:@" "];

UInt8 bytes[dataArr.count];

for (NSInteger i = 0; i< dataArr.count; i++) {

    NSString *obj = dataArr[i];

    UInt8 byte = (UInt8)strtoul([obj UTF8String],0,16);

    bytes[i] = byte;

}

// NSData *data = [NSData dataWithBytes:bytes length:dataArr.count];