Application Notes

Building a Fragmented Message

writing the All Frame Mode Packet to the FLEXchip IC with the “DAF” bit = 1. If no other fragments, temporary addresses are pending or the FAF bit is clear in the All Frame Mode Register, then the FLEXchip IC returns to normal operation.

4.The FLEXchip IC continues to decode all of the frames and passes any address information, vector information and message information to the host followed by a status packet indicating the end of the frame. If the message is indicated as fragmented by the Message Continued Flag “C” in the Message Packet for a Secure, Alphanumeric or Hex/Binary Message then the host remains in the Receive mode expecting more information from the FLEXchip IC.

5.After the host receives the second and subsequent fragment with the Message Continued Flag “C” = 1, it should decrement the All Frame mode counter by sending an All Frame Mode Packet to the FLEXchip IC with the “DAF” bit = 1. Alternatively, the host may choose to decrement the counter at the end of the entire message by decrementing the counter once for each fragment received.

6.When the host receives a Message Packet with the Message Continued Flag “C” = 0, it will send two All Frame Mode Packets to the FLEXchip IC with the “DAF” bit = 1. The two packets decrement the count for the first fragment and the last fragment. This decrements the All Frame mode counter to zero, if no other fragmented messages, or temporary addresses are pending or the FAF bit is clear in the All Frame Mode Register, and returns the FLEXchip IC to normal operation.

7.The above process must be repeated for each occurrence of a fragmented message. The host must keep track of the number of fragmented messages being decoded and insure the all frame mode counter decrements after each fragment or after each fragmented message.

Table C-4 Alphanumeric Message Without Fragmentation