BS EN 62026-7-2013 pdf download.Low-voltage switchgear and controlgear – Controller . device interfaces ( CDIs ) Part 7 : CompoNet.
Fragment count: This marks each separate fragment so that the receiver can identify if any fragment is missed. The Fragment Count increments by one (1) for each successive fragment received. The counter goes back to zero (0) when it reaches the value 256 (fragmentCount = (fragmentCount + 1) mod 256).
If the Fragment type is not 0, it means the transmission is only a portion of the Explicit Message, not the entire message.
Message fragmentation Is performed as a data-link level acknowledgement. The receiver returns only data-link level acknowledgments for every fragment.
The transmitting side functions as specified below:
The sender formulates the message header by setting the Control Code, the Extended SID and SID fields to the value specified by the Application. It initializes the MAC ID fields and other fields. See 5.2.3.2.
• The sender then places the appropriate Fragmentation Protocol information Into the message. The sender stores the Fragment Count that is inserted into the message. The first fragment and middle fragments shall be a full-sized A_EVENT. Otherwise a non- fragmented message or the last fragment shall be used.
• The sender then takes the next piece of the Service Data and places it Into the message.
• If the sender is a slave or repeater, it sets the bit A_EVENT sending request” in its CN frames to inform the master that it needs to send a message. It starts its Explicit Message Timer if this is the first transmission of the message.
• The sender transmits the message and waits for a positive data-link level acknowledgement.
• If no positive acknowledgement is received, the sender retries the last transmission. The retry mechanism is defined in 5.2.4. If the retries fail, then the Application is informed that an error has been detected and the requested transmission cannot take place.
If a positive acknowledgment Is received, then the sender continues normal processing. If the sender is a slave or repeater, the reception of a positive acknowledgement clears “A_EVENT sending request” bit in its CN frames.
The initial state associated with the receiving side entails waiting for either the First Fragment In a fragmented transmission or waiting for the reception of a complete Explicit Message.
The receiving side functions as specified below:
a) If the message header indicates that this is a fragmented Explicit Message, then the receiver examines the Fragmentation Protocol to determine its validity. If the receiver has yet to receive the first transmission in the series (in the initial state) and the Fragment field is not equal to First Fragment, then the fragment is dropped.
b) If It is a single frame message and the Fragment Count is 13, the receiver does the following:
• processes the message, and
• resets to the initial state.
c) If the Fragment indicates that this is the First Fragment, then the Fragment Count shalt equal zero (0) and it is full-sized. If this is the case, then the message fragment is stored. If the Fragment indicates First Fragment and the Fragment Count is not zero (0), then the fragment is dropped.
d) If the Fragment Count is one (1) greater than the previously received count and the Fragment indicates that this Is the Middle Fragment or Last Fragment, the SID is the same as previously received SID and it is a full-sized fragment, then the next fragment has been received. The fragment is appended to the previously received fragment(s). The Fragment Count associated with this fragment is stored.
e) If the Fragment Count is same as the previously received count, the SID is same as previously received SID. and the Fragment does not indicate that this is the First Fragment, then a resent fragment has been received. No action is needed.
f) If the Fragment Count is neither one (1) greater nor equal to the previously received count, then the fragment is discarded. The receiver resets to the initial state.
g) When the last fragment is received the receiver continues processing the message
The EventlAction Matrices presented in Table 36 and Table 37 provide formal definitions of the transmitting and receiving sides of the Fragmentation Protocol.BS EN 62026-7-2013 pdf download.