MC68181 Datasheet, PDF (112/119 Pages) Freescale Semiconductor, Inc – Advance Information ROAMING FLEX chip SIGNAL PROCESSOR

MC68181
Freescale Semiconductor, Inc.
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 page A-7.
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
V₂V₁V₀
000
101
110
Type
Secure
Alphanumeric
Hex / Binary
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 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
C-8
MC68181 Technical Data Sheet
MOTOROLA
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