Application Notes

Building a Fragmented Message

BUILDING A FRAGMENTED MESSAGE

The longest message that will fit into a frame is eighty-four code words total of message data. Three alpha characters per word yields a maximum message of 252 characters in a frame assuming no other traffic. Messages longer than this value must be sent as several fragments.

Additional fragments can be expected when the “continue bit” in the 1st Message Word is set. This causes the pager to examine every following frame for an additional fragment until the last fragment with the continue bit reset is found. The only requirement relating to the placement in time of the remaining fragments is that no more than thirty-two frames (1 minute) or 128 frames (4 minutes) as indicated by the service provider may pass between fragment receptions.

Each fragment contains a check sum character to detect errors in the fragment, a fragment number 0, 1, or 2 to detect missing fragments, a message number to identify which message the fragment is a part, and the continue bit, which either indicates that more fragments are in queue or that the last fragment has been received. All of this information is described in FLEX Message Word Definitions on A-4.

The following describes the sequence of events between the host and the FLEXchip IC required to handle a fragmented message:

1. The host receives a vector indicating one of the following types:

Table C-3 Message Type Definition

2.The FLEXchip IC increments the All Frame mode counter inside the FLEXchip IC and begin to decode all of the following frames.

3.The host receives the Message Packet(s) contained within that frame, followed by a Status Packet. The host must decide based on the Message Packet to return to normal decoding operation. If the message is indicated as fragmented by the Message Continued Flag “C” being set in the Message Packet for a Secure, Alphanumeric or Hex /Binary Message, then the host does not decrement the All Frame mode counter at this time. The host decrements the counter if the Message Continued Flag “C” is clear by