iOS bluetooth Questions - ios

Question

I want to use my iPad to connect with a OLS426 Bluetooth low energy module to send data thorough the serial port on the Bluetooth module. I have successfully connected to the Bluetooth module. In the connection, the iPad is working as a central and the Bluetooth module as a peripheral.
Here are my questions:
(1)
[peripheral setNotifyValue:YES forCharacteristic:characteristic];
I subscribe to the Bluetooth module in didDiscoverCharacteristicsForService.
- (void)peripheral:(CBPeripheral *)peripheral didUpdateNotificationStateForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error{
NSLog(#"Subscribed");
}
After subscribing, the "Subscribed" log is printed on the terminal. Does it mean that I have successfully subscribed to the device?
(2)
I also try to write value for a characteristic in the didDiscoverCharacteristicsForService.
[peripheral writeValue: data forCharacteristic:characteristic type:CBCharacteristicWriteWithResponse];
Since I have set the type to be CBCharacteristicWriteWithResponse, I think that if the writing is not successful, there will be an error. However, there is no error.
- (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error{
NSLog(#"Hello sent");
}
My question is why the "Hello sent" is not printed after I set a value for a characteristic?
(3)
I want to send some data thorough the serial port on the bluetooth module. I can only read data from a characteristic, like a heart rate monitor, or write data to a characteristic. In the services of the Bluetooth module, I find one called the "Serial Port" under which there is a characteristic called "FIFO". So I guess that I should write data to that characteristic in order to send data thorough the serial port. Can anyone tell me if my thinking is correct?

Answer 1

1) Yes.
2) didUpdateValueForCharacteristic is called when the characteristic value changes independently of your own write to that characteristic.
3) Have you read the connectBlue document on how to read/write data via the FIFO characteristic?