获取校验和方法

- (Byte)CalCheckSum2:(NSData *)data{
    Byte chksum = 0;
    Byte *byte = (Byte *)[data bytes];
    for (NSUInteger i = 0; i < [data length]; i++){
        chksum += byte[i];
    }
    return chksum;
}

我的需求：指令是13位byte数组，最后一位是前面十二位的校验和，第三四位是时间（24小时制）小时和分钟转换成的byte字节，其他的都是固定的指令。我的构造方法是

//防盗器 定时充电指令
- (void)onTimeChargeByBlueWith:(NSString *)timeStr
{
    NSArray *array = [timeStr componentsSeparatedByString:@":"];
    
    Byte onTimeChargeOrder[13] = {0};
    onTimeChargeOrder[0] = 0xB9;
    onTimeChargeOrder[1] = 0x60;
    onTimeChargeOrder[2] = [self getByteWithIntString:array[0]];
    onTimeChargeOrder[3] = [self getByteWithIntString:array[1]];
    onTimeChargeOrder[4] = 0x00;
    onTimeChargeOrder[5] = 0x00;
    onTimeChargeOrder[6] = 0x00;
    onTimeChargeOrder[7] = 0x00;
    onTimeChargeOrder[8] = 0x00;
    onTimeChargeOrder[9] = 0x00;
    onTimeChargeOrder[10] = 0x00;
    onTimeChargeOrder[11] = 0x00;
    onTimeChargeOrder[12] = [self CalCheckSum2:[NSData dataWithBytes:onTimeChargeOrder length:12]];
    
    NSData *data = [NSData dataWithBytes:&onTimeChargeOrder length:sizeof(onTimeChargeOrder)];
    
    NSLog(@"构造完的数据是 %@",data);
//这里可以拿到data，然后对蓝牙的peripheral对象调用writeValue方法
//    [self.currPeripheral writeValue:data forCharacteristic:self.characteristic type:CBCharacteristicWriteWithResponse];
    
}

#pragma mark-----------工具方法----------------

- (Byte)getByteWithIntString:(NSString *)intString
{
    int hourInt = [intString intValue];
    Byte hourByte[4]  ={0};
    hourByte[0] = (char)(hourInt >>24 & 0xff);
    hourByte[1] = (char)((hourInt >> 16) & 0xff);
    hourByte[2] = (char)((hourInt >> 8) & 0xff);
    hourByte[3] = (char)((hourInt) & 0xff);
    return (char)((hourInt) & 0xff);
}
// 获取校验和
- (Byte)CalCheckSum2:(NSData *)data{
    Byte chksum = 0;
    Byte *byte = (Byte *)[data bytes];
    for (NSUInteger i = 0; i < [data length]; i++){
        chksum += byte[i];
    }
    return chksum;
}

最后调用方法

[self onTimeChargeByBlueWith:@"13:45"];

得到的数据为

2017-03-11 11:23:21.211 test0227[92358:2093146] 构造完的数据是 <b9600d2d 00000000 00000000 53>