这里以20个字节为一个发送

//写入数据

- (void)writeData:(NSData *)data

{

NSLog(@"send:%@", data);
_responseTimer = [NSTimer scheduledTimerWithTimeInterval:_responseInterval target:self selector:@selector(timeoutForResponse) userInfo:nil repeats:NO];
if (self.writingChar && self.notifyChar)
{
    int len = (int)[data length];
    //当写入的数据大于20个字节时，分包发送
    if (len > 20){
        /**
       *  subdataWithRange( , );
       *  @param 0  从第0个字节开始截取
       *  @param 20 截取数据长度为20
       */

       NSData *dataTemp = [data subdataWithRange:NSMakeRange(0, 20)];

       /**
       dataTemp:           写入的数据
       self.writingChar:   写给哪些特征
       CBCharacteristicWriteWithResponse:   通过此响应纪录是否写入成功
       */

       [self.cbPeripheral writeValue:dataTemp forCharacteristic:self.writingChar   type:CBCharacteristicWriteWithResponse];

       /**
       举例:
       if(len == 43),则 len / 20 == 2;
       i == 0;
       i == 1;
       if(i == 0), 则 len - (20 + 20 * i) == 23;
       if(i == 1), 则 len - (20 + 20 * i) == 3;
       */

       //这里分包发送
       for (int i = 0; i < len / 20; i++)
       {
             int lenTemp = 20;
             if ((len - (20 + 20 * i) < 20) && (len - (20 + 20 * i) > 0)) {//i == 1
                    lenTemp = len - (20 + 20 * i);
             }
             if (len - (20 + 20 * i) > 0){//i ==0;
                   dataTemp = [data subdataWithRange:NSMakeRange(20 + 20 * i, lenTemp)];
                   dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.02 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                   [self.cbPeripheral writeValue:dataTemp forCharacteristic:self.writingChar type:CBCharacteristicWriteWithResponse];
                   });
             }
         }
   }else{//小于20个字节时，直接写入
      [self.cbPeripheral writeValue:data forCharacteristic:self.writingChar type:CBCharacteristicWriteWithResponse];
   }
   dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.02 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
   Byte b[] = {3};
   [self.cbPeripheral writeValue:[NSData dataWithBytes:b length:1] forCharacteristic:self.notifyChar type:CBCharacteristicWriteWithResponse];
   });
}else{
    NSLog(@"木有找到");
    self.sendData = data;
    [self.cbPeripheral discoverServices:nil];
}
}