>>"First i want to know what is the difference between write and WriteWithoutResponse in BLE Properties? my mean is How a BLE can response a Central device?"
--> If PSoC 6 BLE Client wants to write to the BLE Server it can write through Write or WriteWithoutResponse.
--> When Client uses Write API the server has to respond with WriteResponse(). The client will receive event corresponding to write response also. From this the Client application understands that write has happened successully.
--> When client uses writewithoutresponse the server need not has to send the response or acknowledgement.
>>"what is Attribute MTU size? is it related to Response to the central device?"
--> MTU means Maximum Transmission Unit. It is the amount of data that is transmitted in one Transmission unit. Link layer and physical layer handles this. You can keep this at maximum (512).
>>"is Only 20 Bytes but the data is almost large ?"
--> No. It is not large. You can transmit easily. The maximum size of characteristic can be 512 bytes.
>>"How can i read it continuously and show it in my own C# application?"
--> This can be done in 2 ways.
1. Your Client can read the data at fixed intervals. You have to use GATTRead APIs for this.
2. Your server can also send data to client whenever necessary. For this you have to use notification. Notification is similar to Write but the direction is from Server to Client.
For your application, you have to write the I2C data into the characteristics of the server. Then the client can read the data or server can send the notifications.
I hope the above explanation helps. Please refer PSoC Creator code examples on BLE. These helps you to understand the firmware flow of BLE. Also please refer BLE throughput code example from the link below. This helps you to understand how to use Notification API.